Resting spore formation of aphid‐pathogenic fungus Pandora nouryi depends on the concentration of infective inoculum

Abstract

Resting spore formation of some aphid-pathogenic Entomophthorales is important for the seasonal pattern of their prevalence and survival but this process is poorly understood. To explore the possible mechanism involved in the process, Pandora nouryi (obligate aphid pathogen) interacted with green peach aphid Myzus persicae on cabbage leaves under favourable conditions. Host nymphs showered with primary conidia of an isolate (LC(50): 0.9-6.7 conidia mm(-2) 4-7 days post shower) from air captures in the low-latitude plateau of China produced resting spores (azygospores), primary conidia or both spore types. Surprisingly, the proportion of mycosed cadavers forming resting spores (P(CFRS)) increased sharply within the concentrations (C) of 28-240 conidia mm(-2), retained high levels at 240-1760, but was zero or extremely low at 0.3-16. The P(CFRS)-C relationship fit well the logistic equation P(CFRS) = 0.6774/[1 + exp(3.1229-0.0270C)] (r(2) = 0.975). This clarified for the first time the dependence of in vivo resting spore formation of P. nouryi upon the concentration of infective inoculum. A hypothesis is thus proposed that some sort of biochemical signals may exist in the host-pathogen interaction so that the fungal pathogen perceives the signals for prompt response to forthcoming host-density changes by either producing conidia for infecting available hosts or forming resting spores for surviving host absence in situ.

The role of temperature onin vivoresting spore formation of the aphid-specific pathogenPandora nouryi(Zygomycota: Entomophthorales) under winter field conditions

“…Considering that most field temperatures during this survey were below 108C, this phenomenon observed in a laboratory study indirectly supports our result that temperature is the main factor regulating RS production under field conditions. The survival and propagation of an obligate aphid pathogen depends on host density, and the survival strategy for P. nouryi encountering the decrease of available hosts possibly relies on increasing RS formation in vivo (Huang and Feng 2008;Zhou and Feng 2010). Thus, environmental factors that influence host population fluctuation probably regulated the level of fungal RS formation in the field.…”

“…Cadavers were then squashed in lactophenol cotton blue and microscopically examined at 100) magnification to determine the presence of P. nouryi mycosis (cadavers) and RS produced in cadavers. RS were identified as spherical spores, 26.3 mm in diameter (range, 22.5Á32.5 mm), with walls 4.5 mm thick (range, 3Á5 mm), according to Huang and Feng (2008) and Keller (2006). The numbers of cadavers collected on weekly sampling occasions were recorded, and the proportions of cadavers containing RS were calculated.…”

“…Other abiotic and biotic factors reported to influence pathogenÁhost interactions include photoperiod (Hajek and Shimazu 1996), host age (Wilding and Lauckner 1974;Hajek and Shimazu 1996), and host sex (Wilding and Lauckner 1974). Moreover, bioassay data after modeling analysis recently revealed that the probability of P. nouryi RS formation in the host M. persicae increased with inoculum level and this dependence was regulated by temperature and photoperiod (Huang and Feng 2008;Zhou and Feng 2010).…”

Abiotic and Biotic Factors Affecting Resting Spore Formation in the Mite PathogenNeozygites floridana

“…In a field study, Thomsen and Eilenberg [19] found that Entomophthora muscae (Cohn) Fresenius forms resting spores only in female Delia radicum (L.) and that the proportion of females with resting spores was negatively correlated with day length. Further, Huang and Feng [18] hypothesized that the resting spore formation of the aphid pathogenic fungus Pandora nouryi (Remaudière and Hennebert) Humber depends on the inoculum concentration. Later, Zhou and Feng [17] tested the effects of three parameters on the resting spore formation of P. nouryi .…”

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

“…Most of the fungal species never form resting spores in vivo or in vitro . Exceptionally, P. nouryi may form resting spores in vivo (Keller 2006) and was found producing azygospores in cadavers of green peach aphid, Myzus persicae , in China (Huang and Feng 2008).…”