Progress 10/01/04 to 09/30/05
Outputs
Meloidogyne mayaguensis, a highly virulent root-knot nematode, was recently reported infecting various horticultural and ornamental plants in Florida. M. mayaguensis is capable of breaking root-knot nematode resistance genes in tomato, sweet potato, and soybean and also induce more severe disease on many economically important crops compared to other common root-knot nematodes. Our objective were to determine the nematodes pathogenicity relative to other common species found in Florida, namely M. arenaria, M. incognita and M. javanica. Microplots were inoculated with two levels of each nematode (low = one second-stage juvenile (J2) or egg/g of soil, high = three J2 or eggs/g of soil). Cv. Solar set tomato was grown in the microplots for 82 days. The plants were removed and nematode densities in soil, percentages of roots galled, eggs, and plant fresh weights and heights were recorded. M. mayaguensis had a greater number of eggs than all other Meloidogyne spp. with the
exception of M. arenaria (P = 0.05). M. mayaguensis also had a greater percentage of root galling at both inoculum levels, 95% and 99% for low and high, respectively. The size of galls induced by M. mayaguensis was unusually large compared with the other three species. M. arenaria had a greater number of J2 in soil than all other Meloidogyne spp. Fresh weight and height of plants were not different among treatments.
Impacts
We are understanding the nematodes distribution and its threat to Florida agriculture. Because the nematode has the ability to break nematode resistant genes means it poses a serious threat to our horticultural and agronomic crops throughout Florida.
Publications
- Brito, J. A., T. Powers, P. G. Mullin, R. N. Inserra, and D. W. Dickson. 2004. Morphological and molecular characterization of Meloidogyne mayaguensis isolates from Florida. Journal of Nematology 36:232-240.
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Progress 09/15/03 to 09/14/05
Outputs
OUTPUTS: A total of 327 root samples were colleted from agronomic and horticultural crops in Florida, and weeds associated with those crops. Isozyme phenotypes, esterase (EST) and malate dehydrogenase (MDH), were used to characterize and identify the Meloidogyne spp. Female nematodes from each sample were examined using PAGE. Nineteen major bands of EST activity were found, corresponding to 12 phenotypes. A species specific EST phenotype was consistently associated with M. arenaria, M. floridensis, M. graminicola, M. hapla, M. incognita, M. javanica, M. mayaguensis, and M. partytila. Five bands of MDH activity and four phenotypes were also found among the populations; however, as previously known this enzyme had limited diagnostic value for separation of Meloidogyne spp. During this survey, new host records were established for two recently reported root-knot nematode (rkn) species in Florida, M. floridensis and M. mayaguensis (Mm). Plant species found as new hosts of M. floridensis
were Cucumis sativus, Phaseolus sp., Solanum melongena and one weed species, Emilia sonchifolia; whereas for Mm new hosts included Carica papaya and Citrullus lanatus, and three weeds, Eclipta prostrata, Fatoua villosa and Panicum sp., and also one unidentified weed species belonging to family Acanthaceae. M. mayaguensisI, which is of great concern because of its ability to reproduce on rkn resistant crops, was found in 10 counties in Florida. Experiments were conducted to determine whether Mm from Florida was able to reproduce on tomato, pepper, peach and cotton genotypes carrying rkn resistance genes. Tomato and pepper genotypes tested included BHN 543, BHN 585, BHN 586, Sanibel and Charleston Bell, lines 9913/2, SAIS 97.9001, SAIS 97.9008, respectively. Rutgers tomato and Keystone Resistant Giant bell pepper were used as susceptible controls. Six commonly known peach rootstocks and rkn resistant cotton genotypes were evaluated. M. mayaguensis reproduced on all tomato cultivars
regardless of soil temperature, whereas M. incognita reproduced well only at 33 C. Minimal or no reproduction of M. incognita was observed on Mi-1 carrying tomato. Sanibel tomato was susceptible to all isolates of Mm. Isolates of Mm were able to overcome the Mi-1 resistance in four tomato genotypes, and the N-resistance gene in Charleston Belle and the tabasco gene in pepper lines 9913/2, SAIS 97.9001, and SAIS 97.9008. All peach rootstocks were rated as poor hosts of Mm. Lovell generally supported greater numbers of Mm eggs per plant and eggs per gram of root, whereas Flordaguard supported no nematode reproduction. Experiments showed that gall and egg mass indices, eggs per gram of root, and reproductive factor (Rf) differed significantly between cotton genotypes resistant or susceptible to M. incognita (Mi)when inoculated with Mi but not when inoculated with Mm. Resistance to Mi in cotton does not confer resistance to Mm; however, on cotton susceptible to Mi, inoculation with Mm
resulted in gall and egg mass indices, eggs per gram of root, and Rf less than on plants inoculated with the same number of Mi. On cotton resistant to Mi, the two nematode species produced a similar Rf.
PARTICIPANTS: Janete Brito, Nematology, Division of Plant Industry, Florida Department of Agricultural and Consumer Services. Ramandeep Kaur, Post Doctorate Associate. Provided professional training in plant nematology for Dr. Kaur.
TARGET AUDIENCES: Scientific community informed on distribution of Meloidogyne mayaguensis in Florida. County extension personnel informed about distribution of Meloidogyne mayaguensis in Florida. County extension personnel informed about potential threat that Meloidogyne poses to agricultrual in Florida.
Impacts
Meloidogyne mayaguensis, a highly virulent root-knot nematode species, was first reported in the continental USA 5 years ago. The nematode is now known to occur in 10 Florida counties. Meloidogyne mayaguensis breaks root-knot nematode resistant genes in several important agricultural crops. This means this species poses a threat when farmers rely on root-knot nematode resistant crops. All resistant cultivars or genotypes of tomato, and pepper proved to be highly susceptible to M. mayaguensis. Six peach rootstocks were rated as poor hosts for M. mayaguensis.
Publications
- No publications reported this period
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