First Report of a Member of Aster Yellows Phytoplasma Group and of Clover Proliferation Phytoplasma Group Associated with Onion in Texas

An unknown disease(s) emerged this spring (2000) in an onion field in southwestern Texas. Infected onion plants exhibited two symptom types, one with shoot proliferation, moderate stunting of plants, and light yellowish discoloration on leaves (A) and the other with only severe stunting of the plants (B). The bulbs of the infected plants collected from both symptom types were smaller than normal. When the aerial shoots were trimmed, the infected (but not asymptomatic or the severely stunted) bulbs produced multiple slender sprouts after storage in room temperature for about a month. These symptoms are characteristic of yellows diseases caused by phytoplasmas. Ten symptomatic (six with symptom type A and four with symptom type B) and ten symptomless onion plants were collected in early May from an onion field about 1 to 2 weeks prior to blooming. Total nucleic acid was extracted from 0.5 g of shoot tissues from each sample. Nested polymerase chain reaction (PCR) using universal primer pairs (P1/P7 followed...