Root environment is a key determinant of fungal entomopathogen endophytism following seed treatment in the common bean, Phaseolus vulgaris

The common bean is the most important food legume in the world. We examined the potential of the fungal entomopathogens Beauveria bassiana and Metarhizium anisopliae applied as seed treatments for their endophytic establishment in the common bean. Endophytic colonization in sterile sand:peat averaged ca. 40% higher for fungus treatments and ca. six times higher for volunteer fungi (other fungal endophytes naturally occurring in our samples), relative to sterile vermiculite. Colonization by B. bassiana and M. anisopliae was least variable in sterile vermiculite and most variable in sterile soil:sand:peat. The impact of soil sterilization on endophytic colonization was assessed in a separate experiment using six different field-collected soils. Soil sterilization was the variable with the largest impact on colonization (70.8% of its total variance), while the fungal isolate used to inoculate seeds explained 8.4% of the variance. Under natural microbial soil conditions experienced by common bean farmers, seed inoculations with B. bassiana and M. anisopliae are unlikely to yield predictable levels of endophytic colonization.

The genomic and biological characterization of Citrullus lanatus cryptic virus infecting watermelon in China

A dsRNA virus was detected in the watermelon (Citrullus lanatus) samples collected from Kaifeng, Henan province, China through the use of next generation sequencing of small RNAs. The complete genome of this virus is comprised of dsRNA-1 (1603nt) and dsRNA-2 (1466nt), both of which are single open reading frames and potentially encode a 54.2kDa RNA-dependent RNA polymerase (RdRp) and a 45.9kDa coat protein (CP), respectively. The RdRp and CP share the highest amino acid identities 85.3% and 75.4% with a previously reported Israeli strain Citrullus lanatus cryptic virus (CiLCV), respectively. Genome comparisons indicate that this virus is the same species with CiLCV, whereas the reported sequences of the Israeli strain of CiLCV are partial, and our newly identified sequences can represent the complete genome of CiLCV. Futhermore, phylogenetic tree analyses based on the RdRp sequences suggest that CiLCV is one member in the genus Deltapartitivirus, family Partitiviridae. In addition, field investigation and seed-borne bioassays show that CiLCV commonly occurs in many varieties and is transmitted though seeds at a very high rate.

Seed-borne Brachycladium penicillatum Intercepted under Plant Quarantine Inspection in Korea

A fungus detected from the importing seeds of Papaver rhoeas under plant quarantine inspection in Korea was identified as Brachycladium penicillatum Corda. It differed in morphological characteristics from a similar species, B. papaveris, which was known to form no macroconidiophores and no microsclerotia. Since the first interception in 2006, this fungus has frequently been found from importing seeds of Papaver spp. It was detected from 31 out of 282 seed consignments imported from 2006 to 2011. To prevent its introduction to Korea, the seed consignments infested by B. penicillatum were destroyed or reshipped.

The Effect of Seed-borne Mycoflora from Sorghum and Foxtail Millet Seeds on Germination and Disease Transmission

The seed-borne mycoflora of sorghum and foxtail millet collected from different growing areas in South Korea were isolated and taxonomically identified using dry inspection, standard blotter and the agar plate method. We investigated the in vitro and in vivo germination rates of disinfected and non-disinfected seeds of sorghum and foxtail millet using sterilized and unsterilized soil. The percent recovery of seed-borne mycoflora from the seed components of sorghum and foxtail millet seeds was determined and an infection experiment using the dominant species was evaluated for seedling emergence and mortality. A higher number of seed-borne fungi was observed in sorghum compared to that of foxtail millet. Eighteen fungal genera with 34 fungal species were identified from the seeds of sorghum and 13 genera with 22 species were identified from the seeds of foxtail millet. Five dominant species such as Alternaria alternata, Aspergillus flavus, Curvularia lunata, Fusarium moniliforme and Phoma sp. were recorded as seed-borne mycoflora in sorghum and 4 dominant species (Alternaria alternata, Aspergillus flavus, Curvularia lunata, Fusarium moniliforme) were observed in foxtail millet. The in vitro and in vivo germination rates were higher using disinfected seeds and sterilized soil. More seed-borne fungi were recovered from the pericarp compared to the endosperm and seed embryo. The percent recovery of seed-borne fungi ranged from 2.22% to 60.0%, and Alternaria alternata, Curvularia lunata and 4 species of Fusarium were isolated from the endosperm and embryo of sorghum and foxtail millet. Inoculation of the dominant seed-borne fungi showed considerable mortality of seedlings. All the transmitted seed-borne fungi might well be a primary source of infection of sorghum and foxtail millet crops.