Resistance Responses of Plants Regenerated from Peach Callus, Cultures to Xanthomonas campestris pv. pruni

Abstract

<jats:p>A detached-leaf bioassay was used to evaluate peach <jats:italic>[Prunus persica</jats:italic> (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 <jats:italic>Xanthomonas campestris</jats:italic> pv. <jats:italic>pruni</jats:italic> [(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.</jats:p>

Stability of bacterial leaf spot resistance in peach regenerants under in vitro, greenhouse and field conditions

“…This is the first report of germplasm of a tree fruit species, generated from tissue culture, expressing increased levels of disease resistance under field conditions, although several examples of this have been reported for other crop species (Daub, 1986) . To date, research on somaclonal variation has culminated in the release of improved celery (Apium graveolens L.) (Health-Pagliuso et al ., 1989) and sugarcane (Saccha- : Hammerschlag, 1988 andHammerschlag, 1990 ; * Significantly different from 'Sunhigh' (P = 0.05) according to Fisher's LSD test ; TC = tissue-cultured .…”

“…(Krishnamurthi & Tlaskal, 1974 ;Daub, 1986) with increased levels of disease resistance . In the initial selection (Hammerschlag, 1988) and screening (Hammerschlag, 1990) studies, there were numerous regenerants that exhibited somaclonal variation with respect to bacterial spot susceptibility . As the regenerants were monitored over time, following micropropagation and under field conditions, the number of regenerants that continued to express spot resistance decreased .…”

“…Y Means within columns followed by the same letter do not differ significantly (P = 0 .05) according to Duncan's multiple range test . 2 Data from References : Hammerschlag, 1988 andHammerschlag, 1990; * Significantly different from 'Redhaven' (P = 0 .05) according to Fisher's LSD test; TC = tissue-cultured . W Mean separation within columns done by t test at P = 0 .05 .° Fruit severity rating : 0 = no lesions to 5 = > 30% fruit surface affected with a majority of lesions more than 3 mm deep and 5 mm across .…”

“…The 156 series regenerants from 'Sunhigh' embryo # 156 and the 30 and 122 series regenerants from 'Redhaven' embryos # 30 and # 122 were obtained and screened for resistance to X. campestris pv. pruni as described previously (Hammerschlag et al ., 1985 ;Hammerschlag, 1990) .…”

“…Somaclonal variants of peach with increased levels of resistance to X. campestris pv . pruni have been obtained by in vitro selection (Hammerschlag, 1988) and by screening regenerants ex vitro, derived from unselected cells (Hammerschlag, 1990) . Preliminary results from field studies with some of these variants have also been reported (Ritchie et al ., 1993) .…”