Sporulation, storage and infectivity of obligate aphid pathogenPandora nouryigrown on novel granules of broomcorn millet and polymer gel

Abstract

Producing granular cultures of obligate aphid pathogen Pandora nouryi for improved sporulation and storage. Small millet-gel granules were made of the mixtures of 80-95% millet powder with 5-20% polymer gel (polyacrylamide, polyacrylate or acrylate-acrylamide copolymer) and inoculated with mycelia at 30 mg biomass g(-1) dry granules plus 87.5% water, followed by static incubation at 20 degrees C for 4-12 days. The fungus grew well on 12 preparations but best on that including 10% copolymer. An 8-day culture of this preparation discharged maximally 58.5 x 10(4) conidia mg(-1) granule at 100% RH and was capable of ejecting conidia at the nonsaturated regimes of 86-97% RH. During storage at 6 degrees C, granular cultures with >85% water content had twofold longevity (120 days) and half-decline period (34-36 days) of those stored at room temperature. The steadily high water content preserved the cultures better than that decreasing at 6 degrees C. However, conidia from 70-day-stored granules were less infective to Myzus persicae nymphs than those from fresh ones based on their LC(50)s. The millet-gel granules had higher sporulation capacity than reported Pandora cultures and a capability of spore discharge at nonsaturated humidity. The granular cultures are more useful for aphid control.