Responses of potato cultivars to the psyllid (Bactericera cockerelli) under greenhouse conditions

the responses of 20 potato cultivars to the psyllid bactericera cockerelli (= paratrioza cockerelli) were studied under greenhouse conditions. two different trials were conducted, in one two months after planting, 200 adult insects, taken from a phytoplasms-free psyllid colony checked by pcr technique, were released inside a cage in which the potato plants were growing. no insects were placed in a control cage. at the end of the growth cycle following traits were recorded: number of nymphs plant-1, tuber yield (g plant-1) and number of tubers plant-1, also records were made of the degree of internal tuber browning and any abnormal tuber sprouting. in a second trial, psyllid yellows and its capacity to be transmitted in tubers and through grafts were studied in two susceptible cultivars. in the first trial all genotypes showed typical yellowing symptoms on foliage after 15-20 days of exposure to the insect. the number of nymphs among cultivars varied from 90 to 450 plant-1 in 2004 and from 490 to 1800 in 2005. cultivars alpha, gigant, nau-6 and lady rosetta were tolerant since they showed from none to mild internal tuber browning caused by the psyllid. in the rest of the cultivars, discoloration varied from moderate to strong. secondary tuber transmission and serial transmission of psyllid yellows by grafting were not observed; neither foliar symptoms nor internal browning were detected, and sprouting was normal. in both years, yield and number of tubers were significantly reduced by b. cockerelli in all cultivars. internal browning, premature sprouting, lack of sprouting, and hairy sprouts were all induced by the psyllid under greenhouse conditions in the absence of the phytoplasms associated with purple top disease.