Phytophthora spp. Associated with Appalachian Oak Forests and Waterways in Pennsylvania, with P. abietivora as a Pathogen of Five Native Woody Plant Species

To document the distribution of potentially harmful Phytophthora spp. within Pennsylvania, the Pennsylvania Department of Agriculture collected 89 plant, 137 soil, and 48 water samples from 64 forested sites during 2018 to 2020. In total, 231 Phytophthora strains were isolated using baiting assays and identified based on morphological characteristics and sequences of nuclear and mitochondrial loci. Twenty-one Phytophthora spp. in nine clades and one unidentified species were present. Phytophthora abietivora, a recently described clade 7a species, was recovered from diseased tissue of 10 native broadleaved plants and twice from soil from 12 locations. P. abietivora is most likely endemic to Pennsylvania based on pathogenicity tests on six native plant species, intraspecific genetic diversity, wide distribution, and recoveries from Abies Mill. and Tsuga Carrière plantations dating back to 1989. Cardinal temperatures and morphological traits are provided for this species. Other taxa, in decreasing order of frequency, include P. chlamydospora, P. plurivora, P. pini, P. cinnamomi, P. xcambivora, P. irrigata, P. gonapodyides, P. cactorum, P. pseudosyringae, P. hydropathica, P. stricta, P. xstagnum, P. caryae, P. intercalaris, P. 'bitahaiensis', P. heveae, P. citrophthora, P. macilentosa, P. cryptogea, and P. riparia. Twelve species were associated with diseased plant tissues. This survey documented 53 new plant-Phytophthora associations and expanded the known distribution of some species.

Matsushimamyces, a new genus of keratinophilic fungi from soil in central India

During a collecting trip exploring new habitats and locations for keratinophilic fungi, soil samples were collected from Bohani village in the central Indian state of Madhya Pradesh. Following isolation using a hair baiting technique, one sample yielded an interesting hyphomycetous fungus. The fungus, which could easily be observed under a dissecting microscope, formed prominently large, dark brown to opaque, fusoid conidia on horse hair after 2 mo of incubation. Single-conidial colonies were cultivated on Sabouraud dextrose agar medium by direct transfer, using a fine needle under a dissecting microscope. Morphologically the fungus resembles genera such as Bahugada, Hadrosporium, Manoharachariella, Pithomyces, and Septosporiopsis, but differs with regard to its conidia and conidiogenous cells. Based on its unique morphology, the present collection is described as a new genus, Matsushimamyces, with M. bohaniensis as type species. Phylogenetic analysis of the LSU region placed Matsushimamyces in Latoruaceae (Pleosporales, Dothideomycetes). Furthermore, based on the morphological and phylogenetic similarity (ITS and LSU rDNA), a second species, Polyschema venustum, is also referred to Matsushimamyces.

Persistence of four heterorhabditis spp. isolates in soil: role of lipid reserves

Infective juveniles of four Heterorhabditis isolates (H. bacteriophora HI, H. megidis UK211 and HF85, and H. downesi M245) were stored in moist (pF 1.7) and dry (pF 3.3) loam soil at 20 degrees C for up to 141 days. Survival, assessed by the number of nematodes extracted by centrifugal flotation, declined over time, reaching fewer than 18% alive by day 141 for all but one treatment (H. bacteriophora HI in dry soil). The infectivity of nematodes in soil for Tenebrio molitor also declined over time, roughly in accordance with the decline in numbers of nematodes. Energy reserves of extracted nematodes were assessed by image analysis densitometry. There were differences among isolates both in survival and in the depletion of reserves, and there was a significant correlation between these two parameters, suggesting that the extent to which energy reserves are depleted affects survival or that a common factor influences both. However, significant nematode mortality occurred while levels of reserves remained high, and the maximum reduction in utilizable body content for any treatment was 51%, well above starvation level. Therefore, the decline in numbers of living nematodes and the reduced nematode infectivity in soil cannot directly result from starvation of the nematodes. Survival and infectivity declined more rapidly in moist than in dry soil; one isolate, H. downesi M245, was less affected by soil moisture content than the other three isolates.

Persistence of heterorhabditis infective juveniles in soil: comparison of extraction and infectivity measurements

The persistence of Heterorhabditis megidis in soil was studied over a 4-week period. On days 0, 2, 14, and 28, infective juveniles (IJ) were extracted by centrifugal flotation, Baermann funnel, and baiting of soil with Tenebrio molitor larvae, which were then dissected. Extraction efficiencies on day 0 were 82% by centrifugal flotation, 56% by Baermann funnel, and 19.8% by bait insect. The relative efficiency of the three methods changed over time. The relationship between the density of nematodes in the soil and the proportion recovered by dissection was non-linear. Up to a dose of approximately 60 IJ/insect, less than 12% became established, while at higher doses (up to 200 IJ/insect) the invasion efficiency was 23%. Mortality of bait insects increased from day 0 to day 2, but decreased to day 28. A novel method of assessing soil pathogenicity by preparing a soil density series and calculating the dose of soil or IJ that kills 50% of the bait insects gave a similar pattern. This method is recommended as a means of tracking changes in pathogenicity over time when bait insect mortality in undiluted soil is at or near 100%. Two methods of preparing a series of Heterorhabditis IJ densities in soil, either by diluting the soil itself with IJ-free soil or by adding diluted suspensions of IJ to the soil, resulted in the same bait insect mortalities.