Submitted to: Seed Technology Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/23/2005
Publication Date: 9/1/2005
Citation: Mengistu, A., Reddy, K.N. 2005. Detection of phomopsis spp on weed hosts and its pathogenicity on soybean. Seed Technology. Vol. 27: 97-100. Interpretive Summary: Phomopsis seed decay is caused by one of several Phomopsis spp. and is a major cause of poor seed quality in soybeans in regions where the climate is warm and humid during and after seed maturation. There is growing evidence that some weeds are colonized by Phomopsis sp. and are carriers of this fungus. The objective of this research was to determine if weeds present in soybean fields at Stoneville, Mississippi are infected with Phomopsis sp. and determine if the recovered fungus from these weeds can inflict disease to soybean plants and weeds. Phomopsis sp. was isolated from surface disinfected stems of eclipta, prickly sida, Illinois bundleflower, Texasweed, prostrate knotweed, pitted morningglory, nodding spurge and slender aster. Recovery of Phomopsis sp. from weeds without symptoms indicates that these weeds may serve as symptomless host of this fungus. The fact that isolates of the fungus from eclipta and nodding spurge caused soybean plants to produce disease symptoms indicates that Phomopsis sp. may use these weeds as hosts in spreading the disease in the field. This is the first time disease caused by Phomopsis sp. was detected in these weeds.
Technical Abstract: Phomopsis seed decay is caused by one of several Phomopsis spp. and is a major cause of poor seed quality in soybeans in regions where the climate is warm and humid during and after seed maturation. There is growing evidence that a number of weeds are colonized by fungi including Phomopsis sp. that are pathogenic to soybean. The objective of this research was to determine if weeds present in soybean fields are infected with Phomopsis sp. and determine if the recovered isolates from these weeds are pathogenic to soybean plants and weeds. Phomopsis sp. was isolated from the surface of disinfected stems of eclipta (Eclipta prostrata L.), prickly sida (Sida spinosa L.), Illinois bundleflower [Desmanthus illinoensis (Michx.) Macmill. ex B. L. Robins.], Texasweed [Caperonia palustris (L.) St. Hil.], prostrate knotweed (Polygonum aviculare L.), pitted morningglory (Ipomoea lacunosa L.), nodding spurge (Euphorbia nutans Lag.), and slender aster (Aster exilis Ell). Among the weed isolates, the eclipta isolate was very pathogenic on eclipta, prickly sida, sickle pod and pitted morningglory. The isolate from nodding spurge was moderately pathogenic on sicklepod. Dark lesions ranging from 2 to 6 cm in length were produced by the isolates from soybean, eclipta and nodding spurge on both susceptible soybean genotypes and weeds. Each of the weed isolates produced colonies similar to those produced by soybean isolate of Phomopsis sp. The weed isolates produced alpha conidia, stroma, formed concentric pattern, and produced no perithecia. The size of conidia fell within the range of 1.5-3.5 x 5-9 µm. Therefore, the weed isolates were identified in general as Phomopsis sp. Studies are currently underway to characterize and identify the species using molecular marker techniques. Recovery of Phomopsis sp. from asymptomatic weed tissue indicates that these weeds serve as symptomless carriers of this fungus. This is the first report of the occurrence of Phomopsis sp. on the eight weed species investigated from the field plus palmleaf morningglory and sickle pod.