Recipient Organization
UNIVERSITY OF GEORGIA
200 D.W. BROOKS DR
ATHENS,GA 30602-5016
Performing Department
Horticulture
Non Technical Summary
Each year, pecan growers in the state spend $200 to $300 per acre on fungal sprays to fight pecan scab. The disease develops and spreads during wet weather, particularly when the nut is growing. Nuts infected with pecan scab develop black spots on the shuck. Many will be covered so the entire nut turns black and falls off before it's fully developed.For decades, commercial growers have relied on just two pecan varieties, Stuart and Desirable, for the majority of their pecan production. Both Stuart and Desirable had good resistance to pecan scab when they were initially selected. However, both varieties are now very susceptible to the disease. Over time the fungus has adapted to these cultivars to the extent that Desirable is no longer recommended to plant in the southern half of the state.New pecan cultivars are needed to replace these older cultivars and that is the aim of this breeding program. In addition, new cultivars from this program as well as other sources are tested in a replicated orchards and data is acquired on bloom times, insect and disease resistance, yield and quality of nuts so that growers can determine which cultivars will be most profitable for their farm.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
Continue the breeding program by making crosses between cultivars with key horticultural traits and evaluating the progeny for these traits in order to produce new cultivars adapted to growing conditions in the Southeast.Evaluate germplasm accessions for nut yield and quality and pest resistance to determine their potential as new cultivars for Georgia or as breeding stock.
Project Methods
New pecan cultivars must combine both scab resistance and superior nut quality in order to be successful in the long term in the Southeast. Potential cultivars are selected on the basis of large nut size, high percent kernel, good shelling characteristics, early nut maturity, small cluster size to ensure adequate kernel development, and resistance to scab and aphids. Controlled pollinations are made in the spring of each year by bagging individual flower clusters and injecting pollen into the bag with an aspirator. Seedlings are initially planted in pots in a seedling nursery where they are screened for leaf scab resistance during the first year. Prior to planting in the seedling orchard, seedlings with severe leaf scab infections or poor vigor are discarded. Results from previous years indicate that in some crosses as many as 80% of the seedlings can be eliminated due to scab susceptibility. The remaining seedlings are transplanted into a seedling orchard at a spacing of 10 ft by 15 ft. Seedlings are grown in the orchard for approximately 7-10 years and receive optimal irrigation and mineral nutrition, but minimal pesticide applications. Detailed records are kept for nut size and quality, tree vigor and form, phenology, and disease and insect resistance. Every winter discarded trees are marked and a chipper is brought in to grind up discard trees to make room for new progenies. Selections with cultivar potential are propagated onto rootstocks and grown in replicated trial orchards along with check cultivars to estimate yield potential as well as nut quality, phenology, and insect and disease resistance. Those selections that perform better than the check cultivars are considered for release. UGA trial orchards are managed as commercial orchards. Trees are planted at a 40 foot spacing, which results in significant shading in about 15 years. Trees are irrigated through the use of microjet sprayers, and fertilized and sprayed using UGA guidelines for commercial orchards. One difference from commercial orchards is that we like to see some damage from pests each year so that we can better differentiate cultivars based on resistance to these pests. Because of this, we apply pesticides a little later and lighter than a commercial grower might. Since Tift County is not as prone to scab infection as many areas of the state, we will sometimes skip some of the early and later fungicide sprays. Ideally we like to see at least moderate levels of scab infection on 'Desirable' at the end of the year. We also test at several commercial orchards where trees are managed according to the grower's methods. We evaluate cultivars in three broad areas: productivity, quality, and adaptability. The productivity of any cultivar is, of course, of prime importance. We measure productivity by determining actual tree yield for each tree in the test. Quality of the nut crop produced is highly important in determining the value of a pecan cultivar. We evaluate the quality of the crop of each tree in the test from a 50-nut subsample. From the nut sample we determine nut size, percent kernel, shelling ability, kernel color, packing material adherence (fuzz), kernel shape, and overall attractiveness of the kernel. Adaptability is the final category that we rate. This takes into account several diverse characteristics including disease and insect resistance, harvest date, and pollen release and stigma receptivity dates.