Pulse crops such as chickpeas, lentils, and dry peas are grown widely for human and animal consumption. Major yield- and quality-limiting constraints include diseases caused by fungi and oomycetes. The environmental and health concerns of synthetic fungicides used for disease management, emergence of fungicide-resistant pathogens, and demand for organic pulse crop products necessitate the search for effective alternatives. Safe and environmentally friendly plant-derived essential oils (EOs) have been reported effective against some pathogenic fungi. Growth on EO-amended growth medium and an inverted Petri plate assay were used to determine the effects of 38 oils and their volatiles on mycelial growth and spore germination of important pathogenic fungi and oomycetes: Aphanomyces euteiches, Botrytis cinerea, Colletotrichum lentis, Didymella pisi, D. rabiei, D. lentis, Fusarium avenaceum, Stemphylium beticola, Sclerotinia sclerotiorum, and Pythium sylvaticum. Palmarosa, oregano, clove, cinnamon, lemongrass, citronella, and thyme oils incorporated in media inhibited mycelial growth of all the pathogens by 100% at 1:1,000 to 1:4,000 dilution. In addition, thyme oil (1:500 dilution) showed complete inhibition of conidial germination (0% germination) of F. avenaceum and D. pisi. All seven EO volatiles inhibited mycelial growth of all pathogens by 50 to 100% except for B. cinerea and S. sclerotiorum. EO effects on mycelial growth were fungistatic, fungicidal, or both and varied by EO. EOs show potential for management of major crop diseases in organic and conventional production systems.

Botrytis spp. cause gray mold and are significant pathogens of pulse crops (dry pea, lentil, and chickpea). Seedling infection can result in plant stunting and death. In this study, 100 Botrytis isolates were recovered from pulse crop seed samples that were submitted to the Regional Pulse Crop Diagnostic Laboratory at Montana State University. Nine Botrytis spp. were found to be associated with pulse seeds in Montana based on a combination of cultural characteristics; the amplification of partial sequences of the G3PDH, HSP60, and RPB2 genes; and phylogenetic analysis. Botrytis cinerea (n = 54) was the predominant species, followed by B. euroamericana (n = 22) and B. prunorum (n = 11). There were a few isolates of B. mali and five novel Botrytis spp. that included one cryptic species. To determine the pathogenicity and aggressiveness of the isolates, dry pea cultivar Lifter, lentil cultivar Richlea, and chickpea cultivar Sierra, detached leaves were inoculated using mycelial plugs. Lesion diameter produced by Botrytis isolates on three hosts differed (P < 0.05). Aggressiveness of B. cinerea was high in all three hosts and varied among the tested isolates. Spore inoculations were conducted on greenhouse-grown dry pea, lentil and chickpea plants using one sporulating isolate each of B. cinerea, B. prunorum, and Botrytis sp. 1. Results indicated that these isolates were pathogenic on the tested hosts. This study illustrates that many species of Botrytis are associated with pulse crop seed in Montana and can be aggressive on multiple crops, which may have implications for disease management.

Pythium root rot and damping-off caused by Pythium spp. are important diseases of pulse crops. In a 2016 pathogen survey from dry pea growing fields in Montana, along with commonly known causal agents P. ultimum and P. irregulare, an isolate identified as P. sylvaticum (LPPY17) was isolated from the rhizosphere of a diseased pea plant collected from Valley County, MT. Root rots and damping-off caused by P. sylvaticum have not previously been reported for chickpea, pea, and lentil crops. The isolate LPPY17 was tested for fungicide resistance in vitro, and results indicated a reduced sensitivity to metalaxyl- and ethaboxam-containing fungicides. LPPY17 was also tested for pathogenicity on chickpea, pea, and lentil seedlings in the greenhouse, and the results from the study revealed LPPY17 is capable of causing both root rots and damping-off. Due to the potential pathogenicity and reduced fungicide sensitivity of this species, in the future it will be important to monitor for P. sylvaticum in pulse root rot surveys and diagnostics, because management options may be different from other common Pythium spp.