A detached-leaf bioassay was used to evaluate peach [Prunus persica (L.) Batsch] regenerants derived from zygotic embryo callus cultures of cultivars Sunhigh (susceptible to leaf spot) and Redhaven (moderately resistant to leaf spot) for resistance to Xanthomonas campestris pv. pruni [(E.F. Sm.) Dews], the causal agent of bacterial leaf spot. Regenerants obtained from calli produced on two `Sunhigh' embryos, #61 and #156, and on three `Redhaven' embryos were evaluated. Sixty-four percent of the regenerants derived from `Sunhigh' embryo #156 and 13% of the regenerants derived from `Sunhigh' embryo #61 demonstrated significantly greater spot resistance than `Sunhigh'. Regenerants with resistance greater than `Redhaven' were also obtained from both `Sunhigh' embryos. The frequency of variation in the `Sunhigh' seedling population, with respect to the response to bacterial leaf spot, was not so great as that exhibited by the regenerants derived from `Sunhigh' embryo #156. None of the `Redhaven' seedlings or any of the regenerants derived from `Redhaven' embryos were more resistant than `Redhaven'. These studies suggest that the frequency of somaclonal variation is genetically determined and that screening for somaclonal variation may be a feasible approach to obtaining leaf spot-resistant peach plants.
A detached-leaf bioassay was used to evaluate peach [Prunus persica (L.) Batsch] somaclone 122-1 (derived from callus produced on an immature embryo of peach cultivar Redhaven) for resistance to several virulent strains of Xanthomonas campestris pv. pruni [E.F. Sm.) Dows], causal agent of bacterial leaf spot, and to a virulent isolate of Pseudomonas syringae van Hall pv. syringae, causal agent of bacterial canker. The detached-leaf bioassay was also used to evaluate progeny of 122-1 for resistance to X. campestris pv. pruni virulent strain XP1. Somaclone 122-1 was significantly more resistant to most strains of X. campestris pv. pruni than was `Redhaven', and all of its progeny exhibited high levels of resistance to X. campestris pv. pruni strain XP1. Somaclone 122-1 exhibited significantly higher levels of resistance to Pseudomonas syringae pv. syringae than did `Redhaven' and this resistance was retained over time in the greenhouse and following a 2-year cycle of tissue culture propagation.
W. Patrick Wechter, Mark W. Farnham, J. Powell Smith and Anthony P. Keinath
). Chemical control for most of the bacterial leaf-spot diseases of Brassica crops is limited; indeed, in the three management guides previously referenced above, Ivors (2006a , 2006b ) and Maynard et al. (2003) make no mention of bacterial leaf-spot
Abbasali Ravanlou and Mohammad Babadoost
to the pumpkin industry Plant Dis. 93 772 782 Barak, J.D. Koike, S.T. Gilbertson, R.L. 2001 The role of crop debris and weeds in the epidemiology of bacterial leaf spot of lettuce in California Plant Dis. 85 169 178 Bineeta, S.B. Majumder, S. Kumar, S
Yunwen Wang, Huangjun Lu, Richard N. Raid, Gregg S. Nuessly and Georgy Faroutine
impacts on lettuce production. Bacterial leaf spot (BLS), caused by Xcv , is a devastating disease of lettuce in Florida. This disease was first reported in South Carolina and Virginia in the United States in 1918 ( Brown, 1918 ). Since 1990s, substantial
E.A. Wolf and B. Scully
Brent Rowell, R. Terry Jones, William Nesmith and John C. Snyder
Bacterial spot epidemics, caused by Xanthomonas campestris pv. vesicatoria (Doidge) Dye, continue to plague bell pepper (Capsicum annuum L.) growers in a number of southern and midwestern states. A 3-year study designed to compare cultivars and breeding lines under induced bacterial spot epidemic and bacterial spot-free conditions began soon after the first release of cultivars having the Bs2 gene for resistance to races 1 to 3 of the pathogen. Bacterial spot epidemics were created by transplanting `Merlin' plants (inoculated with races 1 to 3) into plots of each test cultivar at an isolated location in eastern Kentucky. Plots of the same trial entries at a second location were kept free of bacterial spot for 2 of the 3 years of trials; however, a moderate natural epidemic occurred at this location in 1996. Bacterial spot resistance had the greatest impact on yields and returns per acre in the inoculated trials. Cultivars with only Bs1 or a combination of Bs1 and Bs3 were highly susceptible in the inoculated trials. There were statistically significant and economically important differences in resistance among cultivars and breeding lines having the Bs2 gene; some were nearly as susceptible as susceptible checks. Although many Bs2-gene cultivars showed satisfactory levels of resistance, only a few were highly resistant, horticulturally acceptable, and comparable in yields to the best susceptible hybrids in a bacterial spot-free environment.