2012 Annual Report
1a.Objectives (from AD-416):
1. Determine inheritance of resistance to Phytophthora fruit rot in watermelon; and develop breeding lines with resistance to Phytophthora fruit rot and watermelon vine decline.
2. Determine genetic basis of resistance to root-knot nematodes in watermelon, identify molecular markers associated with resistance, and develop resistant breeding lines.
3. Determine genetic basis of resistance to root-knot nematodes in pepper and develop resistant breeding lines.
1b.Approach (from AD-416):
Populations of watermelon segregating for resistance to Phytophthora fruit rot will be generated by crossing a highly resistant selection developed from a Citrullus lanatus var. lanatus accession with susceptible commercial cultivars of C. lanatus. These populations will be phenotyped for reaction to Phytophthora fruit rot to determine inheritance of resistance. Molecular markers closely linked to resistance genes will be identified and used in marker assisted selection (MAS) to develop fruit rot resistant breeding lines. Breadth of resistance in watermelon germplasm and breeding lines will be assessed against isolates of Phytophthora capsici from several Southeastern states. Advanced watermelon germplasm lines resistant to vine decline (caused by the whitefly-transmitted squash vein yellowing virus, SqVYV) will be developed using known sources of resistance to SqVYV in wild watermelon accessions via the pure line selection breeding procedure. The advanced resistant germplasm will be crossed with a susceptible commercial cultivar to develop segregating populations to determine inheritance of resistance to SqVYV. Genetic populations of wild watermelon (Citrullus lanatus var. citroides) segregating for resistance to southern root-knot nematode (RKN, Meloidogyne incognita) will be developed and phenotyped for reaction to RKN to determine the mode of inheritance of resistance. Molecular markers closely linked to the RKN resistance gene(s) will be identified and used for gene mapping and MAS. Watermelon populations segregating for resistance will be developed by crossing RKN-resistant C. lanatus var. citroides with cultivated watermelon, C. lanatus. These populations will be phenotyped for reaction to RKN and MAS utilized to develop RKN-resistant watermelon breeding lines. Sweet peppers (sweet banana, sweet cherry, and Cubanelle types) with resistance to southern RKN will be developed using conventional recurrent backcross breeding procedures to transfer the dominant ‘N’ gene for RKN resistance from resistant bell pepper to sweet pepper. Genetic populations of pepper (Capsicum annuum) segregating for resistance to northern RKN (M. hapla) will be developed by crossing a highly resistant selection from a C. annuum accession with a susceptible commercial C. annuum cultivar. These populations will be phenotyped for root galling and RKN reproduction to determine mode of inheritance of resistance to northern RKN.
Portions of this research are a continuation of our previous project (6659-22000-020-00D) that was recently terminated. The USDA Plant Introduction collection of African horned cucumber (Cucumis metulifer) was evaluated for resistance to M. incognita in replicated greenhouse tests. The most resistant African-horned cucumber lines are also being tested for resistance to M. incognita in field tests. Ten African-horned cucumber lines which had been selected for resistance to root-knot nematodes were evaluated as rootstocks for grafted ‘Athena’ cantaloupe in fields infested with southern root-knot nematodes. A root-knot nematode resistant wild watermelon line was developed for use as a rootstock for grafted seedless watermelon. Four Phytophthora fruit rot resistant watermelon germplasm lines were developed and experiments to release these lines were completed. Additional crosses between Phytophthora fruit rot resistant germplasm lines and susceptible commercial cultivars were made for use in determining the inheritance of resistance. Single plant selections from Squash Vein Yellowing Virus (SqVYV) resistant wild watermelon germplasm lines were made to develop resistant watermelon germplasm. A release notice for a new germplasm line 392291-VDR with SqVYV resistance was submitted for approval by National Program Staff. Crosses between 392291-VDR and susceptible commercial cultivar ‘Charleston Grey’ and ‘Mickey Lee’ were made to develop populations for use in inheritance studies.
Watermelon Vine decline resistant germplasm line. Watermelon Vine decline is a serious disease that has plagued watermelon growers for the past several years and has resulted in losses of over $60 million in southwest and west central Florida. ARS scientists in Charleston, SC, developed a watermelon germplasm line “392291-VDR” with resistance to watermelon vine decline (WVD) which is caused by a whitefly transmitted virus. This resistant germplasm line can be used by breeders to develop watermelon varieties with resistance to this dreaded disease. Development of varieties with resistance to watermelon vine decline will help reduce insecticide use and allow growers to grow a successful crop.
Kousik, C.S., Donahoo, R.S., Hassell, R. 2012. Resistance in watermelon rootstocks to crown rot caused by Phytophthora capsici. Crop Protection. 39:18-25.