PLANT IMPROVEMENT IN CUCURBITA THROUGH INTERSPECIFIC HYBRIDIZATION

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1019740
• Project Start Date: Oct 1, 2019
• Project End Date: Sep 30, 2022
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF NEW HAMPSHIRE
51 COLLEGE RD SERVICE BLDG 107
DURHAM,NH 03824

Performing Department
Agriculture, Nutrition and Food Systems

Non Technical Summary
Winter squash is an important crop throughout the northeastern U.S. Three varietal groups: acorn (C. pepo), buttercup/kabocha (C. maxima), and butternut (C. moschata) currently dominate the commercial market. These three species groups have many similar morphological and culinary traits, but there are also valuable traits unique for each species group. We are using two approaches to utilize unique species traits. In the first approach, we are crossing selected strains of C. maxima with selected strains of C. moschata, thereby combining some of the favorable traits of each species to produce vigorous and productive hybrids. Although the interspecific hybrids evaluated to date lack acceptable eating quality for fresh market use, they are highly productive and potentially useful for the pie and baby food processing industries. Another and perhaps more important use of these squash hybridsis as rootstocks for grafting melon. Melons grafted to these hybrids are resistant to sudden wilt, a disease syndrome that has limited melon production in cooler areas of the Northeast. More importantly, grafted melons anchored to a vigorous interspecific hybrid root system, display a remarkable degree of enhanced vegetative growth and fruit yield, reminiscent of 'hybrid vigor' in corn. Research is needed to develop breeding lines that exhibit good interspecific compatibility for high seed yields and to evaluate new rootstock hybrids for compatibility with different melon varieties being grown in New England and other cooler regions of the northeastern U.S.The second approach is to utilize unique and valuable culinary traits in acorn and butternut squash by using a genetic bridge between the two species to allow the transfer of useful traits from one species to another. Using embryo rescue techniques, we obtained an interspecific cross between butternut and acorn squash in 2016. These initial interspecific hybrid plants were back-crossed to both species to further develop a 'genetic pool' of germplasm displaying fertility in crosses to either butternut (C. moschata) or acorn (C. pepo) squash. Butternut squash is a rich source of carotenoid pigments such as lutein and β-carotene (provitamin A), important in human nutrition. Therefore, we plan to transfer genes for high carotenoid from butternut squash into strains of acorn squash, a species with low carotenoid content. Although butternut is widely grown in the Northeast, in many of the most popular varieties fruit have to be stored for several weeks after harvest to obtain adequate starch breakdown to sugar for good palatability. On the other hand, acorn varieties with good eating quality have a high sugar content at harvest for marketing directly in early autumn and bypassing the necessity of costly storage. A second priority will be to transfer genes for rapid starch breakdown from selected acorn breeding lines into butternut lines. Desirable breeding lines will be intercrossed to produce hybrids for evaluation and possible release as new varieties.On an annual basis, powdery mildew disease (PM) is the most devastating disease of squash. Many varieties have intermediate resistance conferred by the Pm-0 gene, but costly chemical control is still required for suppressing the disease. Two new sources of much higher powdery mildew resistance (PMR) have been acquired from tropical germplasm in the species C. moschata, and we are also working with a third source of resistance, a dominant gene, Pm, present in the wild species, C. lundelliana. These sources of resistance all show genetic dominance, and a goal of this research grant will be to determine the inheritance of the new sources of PM, and the genetic relationship of among the different sources of resistance. In addition, a third use of the genetic bridge between C. pepo and C. moschata will be to transfer genes for improved resistance to PM from NH breeding lines of C. moschata into those of C. pepo. Attaining a level of PMR in varieties of acorn squash and pumpkins approaching that which we have obtained breeding lines of C. moschata, would be a transformative development for growing these cucurbits and reducing dependence on chemical control of this disease.

Animal Health Component

15%

Research Effort Categories

Basic

15%

Applied

15%

Developmental

70%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
202	1429	1081	75%
201	1429	1080	15%
203	1420	1020	10%

Knowledge Area
203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants; 202 - Plant Genetic Resources; 201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
1420 - Melons; 1429 - Cucurbits, other;

Field Of Science
1081 - Breeding; 1080 - Genetics; 1020 - Physiology;

Keywords

winter squash

interspecific hybridization

powdery mildew resistance

carotenoids

grafting melons

Goals / Objectives
Plant breeding research directed towards producing new varieties of squash and pumpkin for fresh market and processing have been ongoing at the University of New Hampshire (UNH) for over 75 years, and during the past 25 years has resulted in the introduction of 14 new varieties of squash into the seed trade. In addition, numerous breeding lines have been made available to interested seed companies. Three major objectives of the breeding research have been to develop early maturing cultivars with a more compact, bush growth habit, improve eating and nutritional quality, and enhance resistance to common pest problems existing in the Northeast. The major effort at improving disease resistance has been incorporating intermediate resistance to powdery mildew conferred by the Pm-0 gene into pumpkin, acorn squash, and butternut squash breeding lines, and resistance to powdery mildew and fusarium wilt into melon breeding lines.One of our more recent breeding projects supported by Hatch grants has been to develop interspecific hybrids, produced by crossing bush strains of C. maxima x vine strains of C. moschata, for use in the processing industry and as rootstocks for melon grafting. We have shown that certain interspecific hybrid combinations have a desirable semi-bush plant phenotype for maximizing leaf canopy cover, exhibit resistance to common pests that plague most squash cultigens and produce prodigious fresh weight yields, out-performing standard processing cultigens of C. moschata. Although the processing industry is reluctant to switch to hybrid varieties, some of these hybrids have been successfully tested as rootstocks for grafting to melon varieties adapted to New England. Grafted melons are resistant to sudden wilt, a disease syndrome that causes wilting of vines as fruit reach maturity. Grafted melon plants often out-yield non-grafted plants by more than double without sacrificing eating quality. In addition, some of our interspecific hybrids flower early and can be used as rootstocks to induce early flowering and fruiting of tropical germplasm that is difficult to reproduce in temperate climates. A relatively low yield of well-filled hybrid seed currently limits commercialization of these hybrids, necessitating research todevelop breeding lines with improved cross-compatibility.As part of our research on interspecific hybridization and improvement of culinary traits in squash, we have recently been able to develop a genetic bridge between the acorn group of squash (C. pepo ssp. ovifera) and the butternut group (C. moschata). Promising initial results suggest that we can use the genetic bridge to transfer important culinary traits between species, and two important goals would be to transfer genes for high carotenoid content from butternut squash into acorn squash, and genes conferring high sugar content from acorn into butternut squash. The genetic bridge can also be used to transfer genes for pest resistance between species. We have identified two new genetic sources of high resistance to powdery mildew (Podosphaera xanthii) in C. moschata. Transferring these resistant traits into C. pepo germplasm could markedly reduce pesticide use for controlling powdery mildew. Successful transfer of these traits will be followed by breeding inbred lines to construct hybrid varieties suitable for introduction into the commercial seed trade.The major objectives of the proposed research on utilizing interspecific hybridization and traditional breeding methods are as follows:Using traditional breeding methods, complete the development of bush C. maxima lines with high seed yields, and further evaluate cross compatibility with C. moschata and grafting compatibility with melon.Determine the inheritance of two new dominant genetic sources of powdery mildew resistance in C. moschata, and their relationship to the Pm-0 gene that confers intermediate resistance.Utilize a genetic bridge established between C. pepo spp. ovifera and C. moschata to transfer culinary traits between species, and transfer genes for improved powdery mildew resistance from C. moschata to C. pepo.

Project Methods
Growing Conditions. Field experiments will be conducted at the Kingman Research Farm (NHAES) in Madbury, NH. Plants will be grown on raised, mulched beds with drip irrigation installed beneath the mulch. Insect and disease control will be according to recommendations given in the most recent New England Vegetable Management Guide. Some breeding and grafting research will be done in the Macfarlane greenhouses during the fall and spring seasons.Interspecific hybrids for rootstocks. Several new inbred processing lines of C. moschata have been developed for use in developing interspecific hybrids using standard pedigree breeding methods. One breeding line in particular, however, Mo116-33-7, has shown exceptionally good cross-compatibility and will be used as the standard parent. In C. maxima, bush lines with high seed yield were developed between 2011 and 2017, but more crosses are needed to establish compatibility with C. moschata. During the summers of 2019 and 2020, further tests of cross-compatibility between C. maxima and C. moshcata will be performed.Use of interspecific hybrids for grafting studies. For grafting studies rootstock NH1349 and selected melon varieties will be seeded in 50-cell plug trays and grown to the first-leaf stage for grafting using the one cotyledon splice-graft method. Seedlings will be kept in appropriate healing chambers at 27 0C under LED blue lighting to maintain stocky plants. After 12 days at the 2-leaf stage, plants will be hardened for two or three days in an unheated greenhouse prior to field transplantation. Data will be collected on vegetative growth and days to first pistillate flowering. During harvest, data will be collected on fruit weight, fruit number, and soluble solids content and notes will be taken on overall visual appearance, including the netting of cantaloupes, flesh firmness, and freedom from cracking.Interspecific transfer of genes for culinary traits. Initial crosses between C. pepo and C. moschata, using embryo rescue to recover seedlings, have largely broken the fertility barriers between the two species. During winter-spring of 2018, we obtained ample seed from six selfed populations resulting from two crosses of an acorn breeding line x an interspecific hybrid population segregating for high carotenoid content. In addition, three selections were backcrossed to an elite inbred acorn breeding line. During summer of 2018, we grew nine populations of plants derived from the greenhouse selfs and crosses, and these populations were used to form genetic bridge populations for transferring high carotenoid content into C. pepo, acorn group, and transferring new sources of PMR into C. pepo. The selfed selections with the highest carotenoid content, along with backcrosses of selections to breeding lines of acorn squash, form the genetic base from which further selection will be made for high carotenoid content in future generations. For achieving more rapid starch degradation and high soluble solids content at harvest in C. moschata, we utilized a selection from a 2017 interspecific hybrid population which had relatively high soluble solids at harvest, Progeny from this selection were grown in the greenhouse in winter/spring of 2018, and one selection (IS20-4-1) was obtained with both high soluble solids (14%) at 52 DAP and high starch content (19.9% DW). This selection was backcrossed to an elite butternut breeding line (Mo204-3-9-16) with PMR. Plants from the field population derived from IS20-4-1 x Mo204-3-9-16 were highly fertile, and several self- and cross-pollinations to elite breeding lines were obtained from plants with high sugar and starch content. These crosses and selections thus represent the initial breeding germplasm from which to obtain elite breeding lines having an acceptable balance of starch and sugar at harvest to circumvent the need for prolonged storage to achieve culinary appeal.Utilization of new sources for powdery mildew resistance. Most of the breeding and genetic effort will focus on utilizing two new sources of relatively high resistance to PM found in an Australian accession of C. moschata, designated Mo148-15-6 (AusPMR), and an accession from a Costa Rica designated OSA (OSA-PMR). Preliminary data suggest that resistance in both of these PMR sources is dominant and that AusPMR is conferred by a single gene, but these inheritance patterns need to be confirmed, We also plan to ascertain if the genes conferring resistance in the above two accessions are non-allelic and assort independently from PMR in C. lundelliana, conferred by a dominant gene (Pm), and the intermediate resistance conferred by the semi-dominant Pm-0 gene. A USDA accession is our source of C. lundelliana PMR (Pm gene). 'Waltham Butternut' (WBN) will be used as the susceptible control cultigen, and for test crosses. We are in the process of developing crosses heterozygous for the different pairs of putative dominant genes for PMR, and in developing testcross populations. We expect to obtain initial inheritance data on allelism and independent assortment of AusPMR and the Pm-0 gene during the summer of 2019, concurrently with obtaining inheritance data for AusPMR. We have developed testcross populations for Pm-0 x Pm (C. lundelliana). The OSA line will be crossed to WBN, C. lundelliana, and Mo148-15-6 in spring of 2019, and testcross populations will be made during summer of 2019. We anticipate future collaboration with molecular geneticists will allow molecular markers to be developed for the different sources of PMR. We plan to initiate field screening for PM during the summer of 2019. Plants will be inoculated by spraying a spore suspension onto the leaves. Powdery mildew ratings will use a previously reported scale whereby 0 = no infection, 1 = 1-20% infection, with the scale continuing to 5 = 80% infection or plant death. For screening Pm-0 we will use genetic markers previously developed by Dr. Mazourek at Cornell. In C. lundelliana, PM resistance produces a hypersensitive reaction in the leaves causing yellow spots, which can be used to identify plants carrying the Pm gene. AusPMR has already been incorporated into some elite breeding lines of C. moschata with round fruit, and this source of PMR is being transferred into butternut lines through backcrossing. We have made initial crosses of plants carrying the AusPMR to the genetic bridge plants of C.pepo/C.moschata), and these plants are being crossed into breeding lines of C. pepo.Pigment analyses. Initial selection for high carotenoid content will be done visually with the aid of a Roche® Egg Yolk Fan (YCF). The Roche YCF has 15 pigmentation hues from 1 through 15. The egg yolk fan is further useful for identifying breeding lines with high carotene content (YCF values of 14 and 15) versus those that contain a large proportion of xanthophylls (YCF 11 to 13), which in C. moschata, comprise mostly nutritionally important lutein. For finished inbred lines of both C. moschata and high carotenoid acorn lines, squash samples will be lyophilized in a freeze dryer and analyzed by HPLC for carotenoid profiles by Creative Proteomics (45-1 Ramsey Road, Shirley, NY 1967). It is anticipated that both elite inbreds and selected hybrids will be evaluated for carotenoid profiles, and any released varieties will be subjected to carotenoid analysis.

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:The target audiences reached by the project includedpersonnel from seed companies, vegetable gardeners, extension educators and researchers. During the reporting period, efforts to reach these audiences included 1) written manuscripts and poster presentations, 2) germplasm releases, and 3) online trainings/presentations. Changes/Problems:In 2020, COVID-19 restrictions prevented us from planting several different projects due to a lack of access to field space. As a result, we delayed some experiments including melon grafting and seed yields of promising rootstocks for grafting. For the things we deemed to be of highest current priority to be included in the field, planting was delayed for almost 3 weeks. This delay may have affected some of our results, specifically our hybrid butternut trials. It was questionable whether squash were able to reach full maturity by harvest. Outreach was also reduced in scope, as we were not able to invite some stakeholders (seed companies) to visit our plots to assess phenotypes and yields of both hybrids and collaborative breeding projects. More significantly, the PD of this project, Dr. JB Loy, passed away after a brief illness in July 2020, leaving a rich legacy but a challenging situation. As such, we have had a change in project director - Dr. R Sideman is now overseeing project personnel to organize and summarize the material and information related to this program and to finish all of the efforts initiated in the current reporting period. As such, we have reoriented our current activities to ensure that the genetic resources developed throughout Dr. Loy's program are curated properly, we are taking several steps to make sure that these resources are properly cared for and that they wealth of knowledge about these materials is not lost. Towards this end, specific new short-term objectives for the next reporting period are: Evaluate seed stocks and conduct germination tests on advanced breeding lines that are either currently licensed to companies or that have potential for future work. This includes lines of melon, summer squash, winter squash, pumpkin and gourd. For advanced breeding lines that have low inventory (<250 seeds) or low viability (<50% germination), develop a plan for growout and seed increase in spring or summer 2021. Develop a document that describes the breeding program systems, procedures and inventory, with the objective that someone unfamiliar with the program could locate a particular item, and know where to look to access notes and data relating to that item. What opportunities for training and professional development has the project provided?Grafting tutorial provided to UMASS extension professional via zoom. August 2020. How have the results been disseminated to communities of interest?Field visits by four seed companies to assess hybrid trials and cooperative breeding projects (Hybrid Seeds, NZ) Growing Melons in NH: Facebook Live Event. Sept 2020. Ask UNH Extension Online Event, and an accompanying extension fact sheet: Growing Melons in NH, Available at https://extension.unh.edu/blog/growing-melons-new-hampshire. What do you plan to do during the next reporting period to accomplish the goals?Objective 1. Using traditional breeding methods, complete the development of bush C. maxima lines with high seed yields, and further evaluate cross compatibility with C. moschata and grafting compatibility with melon. Additional experiments are needed to assess seed yields of currently developed interspecies hybrids. Due to Covid-19 research restrictions, we were unable to conduct trials during the 2020 field season. In summer 2021, we plan to evaluate several promising segregating C. maxima x C.maxima F2 populations for high seed yield and bush growth habit. This will be an important step towards developing candidate female parent lines for interspecific hybrids. Objective 2. Determine the inheritance of two new dominant genetic sources of powdery mildew resistance in C. moschata, and their relationship to the Pm-0 gene that confers intermediate resistance. In 2021, we will continue to use our inoculation and screening methodology to further understand the genetic basis for our various forms of powdery mildew resistance and their relationships. Inheritance of the AusPMR resistance has been determined and efforts with AusPMR will focus on marker assisted backcross breeding to incorporate it into breeding lines. Several selections of butternut squash with good fruit shape and quality and AusPMR have been advanced to F3 and BC2 generations. These selections will be genotyped, grown during Spring 2021, and self-pollinated and backcrossed as appropriate to generate seed for the field season of 2021. Experimental hybrids of C. moschata butternut lines carrying AusPMR will be generated in spring 2021 in the greenhouse for subsequent field evaluation. We will also create hybrids that carry combinations of Pm-0 and AusPMR and screen them for PMR in the field in 2021. For the first time, we will observe the action of AusPMR and Pm-0 combined in a butternut squash background. In other backgrounds, this combination has provided a very high level of resistance. In Spring 2021 we plan to screen segregating backcross and F2 populations containing OSA PMR or C. lundelliana Pm for powdery mildew resistance in the greenhouse at Woodman Farm. Unlike AusPMR and Pm-0, we do not yet have molecular markers for OSA or Pm resistance genes. Selections will be seeded in early January and inoculated at the 5-6 leaf stage. We also plan to grow and evaluate two populations of C. maxima BC4 breeding lines which will segregate for Pm. Inheritance ratios will be calculated, and we will use male flowers from highly resistant segregants to perform additional backcrosses. Progeny from the spring crop will be grown and screened for PMR in the field in summer of 2021. Backcrosses will be performed to WBN to move these lines closer to isogenic status for the different resistant genes. At that point, we expect to collaborate further with molecular biologists to generate molecular markers linked to the remaining resistant genes. Objective 3. Utilize a genetic bridge established between C. pepo spp. ovifera and C. moschata to transfer culinary traits between species, and transfer genes for improved powdery mildew resistance from C. moschata to C. pepo. Culinary Traits. Of the promising selections made in the field in 2020, five acorn selections will be grown out in the greenhouse during the spring of 2021. Several butternut selections from 2020 will be grown in spring 2021 and self-pollinated, to produce progeny with high early sugars for planting during summer 2021. From these, acorn lines with high carotenoid content and desired fruit shape and butternut selections with high-early-sugars will be planted in the field for field evaluation, selection and self-pollination. Carotenoid content, brix at harvest, and various fruit and agronomic characteristics will be assessed. Powdery Mildew Resistance. Marker assisted selection will be utilized in winter/spring 20201 and summer 2021 to move promising lines forward and further backcrosses will be made to a diversity of elite acorn and pumpkin lines. Seeds from those crosses will be screened for the molecular marker prior to planting of spring 2021 greenhouse crops. Only plants with the desired PMR genotype will be grown and used for backcrossing to elite lines. By end of 2021 field season, we should have numerous lines of pumpkin, summer squash, and acorn all carrying AusPMR. Use of this marker assisted backcross system will enable rapid progress breeding a new generation of squash and pumpkins with greatly heightened PMR.

Impacts
What was accomplished under these goals? Objective 1. Using traditional breeding methods, complete the development of bush C. maxima lines with high seed yields, and further evaluate cross compatibility with C. moschata and grafting compatibility with melon. During 2019, several crosses were made between C. maxima lines with high seed yields and C. moschata lines that have shown good cross compatibility with C. maxima cultigens. Data were collected on seed number per fruit and percentage of well-filled seed. Additional experiments are needed to assess seed yields of C. maxima lines that will be used as female parents to create interspecies hybrids; AND to make test crosses and assess seed yields of several different combinations of candidate parents of those interspecies hybrids. Due to Covid-19 research restrictions, we were unable to complete that work during the 2020 field season. In 2020, no additional progress was made on evaluating cross-compatibility with C. moschata and graft compatibility with melon. Objective 2. Determine the inheritance of two new dominant genetic sources of powdery mildew resistance in C. moschata, and their relationship to the Pm-0 gene that confers intermediate resistance. We have been exploring two sources of moderately high resistance to PM, one source from an Australian accession of C. moschata, designated Aus-PMR, and the other from a Costa Rican landrace of C. moschata, designated OSA-PMR. 'Waltham Butternut' (WBN) has been used as the susceptible control cultigen, and for test crosses. The Aus-PMR resistance has been introgressed into several C. moschata breeding lines and appears to be conferred by a single dominant gene. In 2019 and 2020, the testcross and dihybrid populations supported a single dominant gene model for inheritance of Aus-PMR. In the dihybrid cross, plants carrying the Pm-0 allele were identified by a SNP marker, revealing that Pm-0 segregated independently from Aus-PMR. OSA-PMR appears to have a more complex inheritance pattern. PM screening of segregating populations in the greenhouse suggested di-genic inheritance, but further evaluations are required. In a test for allelism between OSA PMR and Pm-0, susceptible segregants were observed at expected ratios which suggests that OSA PMR and Pm-0 are generated by different and independently sorting loci. Field evaluations during 2020 revealed that OSA PMR provides a high level of resistance especially when homozygous. Like AusPMR, OSA PMR appears to be incompletely dominant, as OSA x WBN F1 hybrids how an intermediate resistance compared to homozygous OSA resistance. Progress with Pm from the wild species C. lundelliana is advancing, but slowly. C. lundelliana is very late in its flowering which makes using it for crosses challenging. It also shows limited fertility with our susceptible control line, WBN; viable seed have not been obtained from this cross. If C. lundelliana is used as female parent, the seeds possess an unknown dormancy factor which limits their usefulness. Nonetheless, Pm, has been introgressed into other C. moschata breeding lines and some C. maxima breeding lines. The relationship of Pm to the other resistant genes remains unknown. We obtained preliminary evidence suggesting allelism between Aus-PMR and Pm, but this requires confirmation. Objective 3. Utilize a genetic bridge established between C. pepo spp. ovifera and C. moschata to transfer culinary traits between species, and transfer genes for improved powdery mildew resistance from C. moschata to C. pepo. Culinary traits. As part of our research on interspecific hybridization and improvement of culinary traits in squash, we have been able to develop a genetic bridge between the acorn group of squash (C. pepo ssp. ovifera) and the butternut group (C. moschata). Promising initial results suggest that we can use the genetic bridge to transfer important culinary traits between species. Our two main goals are to transfer genes for high carotenoid content from butternut squash into acorn squash, and genes conferring high early sugar content from acorn into butternut squash; e.g. to develop high-early-sugar butternut and high-carotenoid acorn squash. We've seen an increase in the carotenoid content of several breeding lines of acorn squash created utilizing this genetic bridge in the four generations produced between the winter of 2019 and summer of 2020. Similarly, butternut squash breeding lines created utilizing this genetic bridge have been shown to be higher in soluble solids (brix) at harvest than traditional butternut varieties, which develop high sugars over a period of several weeks. Several selections from promising acorn and butternut breeding lines were made in the field during the 2020 growing season. For butternut, several hybrid combinations utilizing a subset of the high-early-sugar lines were generated in the greenhouse in spring 2020 and were evaluated during in summer 2020. The hybrids evaluated in 2020 did not show high-early-sugar development to the same degree as observed in the parent lines, but possible reasons for this include that fruits were not tagged at anthesis making it necessary to estimate fruit maturity, and the hybrids evaluated came from a small subset of potential parent breeding lines. Powdery mildew resistance. The genetic bridge is also being used to transfer genes for pest resistance between species. We have identified two new sources of high resistance to powdery mildew (Podosphaera xanthii) in C. moschata. Transferring these resistant traits into C. pepo germplasm could markedly reduce pesticide use for controlling powdery mildew. Successful transfer of these traits will be followed by breeding inbred lines to construct hybrid varieties suitable for introduction into the commercial seed trade. Several interspecific crosses were made in the attempt to transfer the AusPMR (Pm-A) gene from C. moschata to C. pepo (pumpkins and acorn squash) via the previously mentioned genetic bridge. A genetic marker was developed for this gene and subsequently, populations can now be screened for the presence of the Pm-A gene. This marker was validated during 2020 was used to select within backcross populations in C. moschata 'Waltham butternut' (WBN), and for selection within segregating populations using other elite C. moschata breeding lines. Marker screening at outset of the field season of 2020 did reveal that AusPMR marker was successfully introgressed into several interspecific hybrids containing acorn squash and pumpkin. Field evaluation confirmed that the plants carrying the AusPMR marker were, in fact, quite resistant to powdery mildew. Plants with the appropriate genotype were backcrossed and crossed to summer squash breeding lines (both crook neck and straight neck), acorn lines, and elite pumpkin breeding lines.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Roman, C, Loy, J.B. Increased fruit size and yield through grafting melons to interspecific rootstocks. Poster for COLSA Undergraduate Research Conference.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Ogden, AB, RG Sideman, and JB Loy. 2020. A single dominant gene, Ef, confers early flowering in acorn squash (C. pepo subsp. ovifera). Cucurbit Genetics Cooperative Report 42:30-36.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2020 Citation: Ohletz, JL and JB Loy. 2020. Grafting melons increases yield, extends the harvest season, and prevents sudden wilt in New England. HortTechnology in press.