Selection of peach cells for insensitivity to culture filtrates of Xanthomonas campestris pv. pruni and regeneration of resistant plants

Abstract

Individual callus cultures were initiated from 400 immature embryos of bacterial leaf spot-susceptible 'Sunhigh' peach. Each was subjected to several selection cycles of a toxic culture filtrate produced by Xanthomonas campestris pv. pruni, the causal agent of leaf spot of peach. Progressively higher concentrations of the filtrate were used in each cycle. Two calli survived, and two plants were regenerated from each of the surviving calli. Each of the four clones was propagated in vitro and tested for whole plant resistance to X. c. pv. pruni. Results from bioassays on greenhouse-grown plants indicated that two out of the four selected clones were significantly more resistant to X. c. pv. pruni than the parental cv 'Sunhigh'. In addition, one clone was significantly more resistant than the moderately resistant cv 'Redhaven'.

Ontogeny of shoot regenerants on excised immature peach embryos

“…Embryo callus cultures have produced regenerative plantlets which when screened against the bacterial spot pathogen, Xanthomonas campestris pv. pruni, exhibited greater pathogen resistance than the donor plants (Hammerschlag 1988). Although the increased disease resistance observed in these studies was attributed to plants derived from embryolike structures, no evidence of the occurrence of somatic embryo genesis was presented.…”

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 .…”

“…pruni (Hammerschlag, 1988) . 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 using a modified detached-leaf bioassay (Hammerschlag, 1988 ;Randhawa & Civerolo, 1985) . Symptoms of infection with X. campestris pv.…”

“…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) .…”