PHOTOPERIOD SOMETIMES INFLUENCES COMMON BACTERIAL BLIGHT DISEASE OF COMMON BEANS

摘要

Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp), is a serious disease of common beans (Phaseolus vulgaris L,). Three experiments were conducted twice in growth chambers at 26 +/- 1C under short (10 hours light/14 hours dark) and long (16 hours light/8 hours dark) photoperiods to determine the influence of these photoperiods, flower bud removal, pod development, and pre- and postinoculation photoperiods on the reaction of common beans to Xcp. In one test, 'PC-50' (susceptible; S) flowered earlier and was more susceptible to Xcp under the Short photoperiod than under the long photoperiod, BAC-S (resistant; R) flowered at the same time under both photoperiods but developed rapid leaf chlorosis (RLC) (hypersensitive reaction) under long photoperiods. Flowering and disease reactions to Xcp by XAN-159 (R) were similar under both photoperiods. In a second test, daily removal of flower buds of 'PC-50' decreased its susceptibility to Xcp under the short photoperiod, RLC of inoculated leaves of BAC-6 occurred during flowering and pod development under both photoperiods. XAN-159 expressed a high level of resistance to Xcp but showed RLC at later pod development stages, In a third test, the disease reaction of 'PC-50' was affected by the particular photoperiod applied post-inoculation but was not influenced by the photoperiod applied before inoculation with Xcp. The implications of these results in breeding beans for resistance to Xcp are discussed.