SELECTION OF SYMPTOM VARIANTS FROM THE NY-MAV STRAIN OF BARLEY YELLOW DWARF VIRUS AND THEIR EFFECTS ON THE FEEDING-BEHAVIOR OF THE VECTOR SITOBION-AVENAE (HOMOPTERA, APHIDIDAE)

Symptom variants were subcultured from the NY-MAV isolate of barley yellow dwarf virus (BYDV) by transmission with single individuals of Sitobion avenae (F.). The aphids were allowed a 3-d acquisition access on infected oats, followed by a 1-h infection feeding access time on individual test plants. Infections were verified by ELISA. Two variant types were identified. Symptoms of one, the "notch" subculture, included the development of notches, leaf twisting, and intense reddish color. Those of the other, the "red" subculture, included only the intense red coloration. These symptom types were maintained through several successive transfers using 5-10 aphids and longer feeding infection times. Greenhouse and electronic monitoring experiments were conducted to evaluate the efficiency with which these variants were acquired from and transmitted to 'Coast Black' oats by S. avenae. Electronic monitoring showed that S. avenae fed better on infected than on healthy plants, with faster and longer phloem contacts. Aphids acquired virus from the plants infected with the red subculture with greatest efficiency and made faster and longer phloem contacts on them than aphids fed on plants with the notch subculture, the source NY-MAV isolate, or on healthy plants. Extracts from plants infected with the red subculture also showed the highest ELISA values, suggesting a greater rate of replication.