Resistance to northern root -knot nematode (Meloidygyne hapla Chitwood) in lettuce (Lactuca sativa L.)
The present study was undertaken to identify lettuce gel' plasm having resistance to M. hapla. Approximately 500 Lactuca accessions were evaluated in the greenhouse for resistance to M. hapla. Six week old seedlings were inoculated with M. hapla at 5,000 eggs per plant. Twelve weeks after inoculation data were recorded on root galling and fresh root weight. The accessions with a root galling score of two or less were considered resistant to M. hapla and were screened in a second trial. Two L. sativa accessions (PI 508476 and PI 419140) and three wild Lactuca accessions, L. saligna PI 281876, L. saligna PI 491000 and L. virosa PI 273579, were identified as putatively resistant to M. hapla. ^ Conventional breeding and induced mutagenesis were used to develop M. hapla resistance in L. sativa cv. Ithaca. Crosses were made in the greenhouse to transfer M. hapla resistance into L. sativa cv. Ithaca from the comparatively M. hapla tolerant L. sativa cv. Salinas. None of the crosses formed a seed. This may indicate that pollen never reached the stigma or that these cultivars are incompatible, a phenomenon common between Lactuca species. ^ Seeds of L. sativa cv. Ithaca were mutated with ethyl methanesulfonate (EMS). 1.5% and 1.75% EMS seed treatment for two hrs showed 40–60% seed germination. The M1 population from these treatments was slow in growth and showed delayed bolting, and the M1 plants were sterile. M1 plants also showed no resistance to M. hapla when inoculated in greenhouse assays. ^ Lettuce root and shoot culture studies were also conducted to find the optimum media that would be helpful for in vitro screening of lettuce germplasm against nematodes and in vitro lettuce plantlet induction, respectively. Statistically, the highest number of root tips and maximum root length was observed on MS and B-5 media supplemented with 6% sucrose. Shoot cultures were initiated in almost all the Lactuca accessions on MS and B-5 media supplemented with 0.44 µM BAP + 0.54 µM NAA+ 3% sucrose. ^
Agriculture, Plant Pathology
"Resistance to northern root -knot nematode (Meloidygyne hapla Chitwood) in lettuce (Lactuca sativa L.)"
Dissertations and Master's Theses (Campus Access).