Variability among biotypes of the Diaporthe/Phomopsis complex of soybeans
Abstract
Morphological, physiological, and pathological characteristics were used to describe variability among the Diaporthe/Phomopsis biotypes common to soybeans in Indiana. One hundred thirty four Indiana isolates collected over a five year period from soybean pod and seed tissues of cultivars in rotations and tillage systems common to the Midwest were studied and compared to 12 selected isolates from other states. Although morphological variability was identified, Diaporthe and Phomopsis types were characterized. Phomopsis isolates predominantly had restrictive stroma, abundant pycnidia with short beaks ($<$200 microns) and conidia with a highly variable length-to-width ratio. Isolates of this type commonly referred to as P. sojae were dominant, whereas the P. longicolla type represented less than 10% of the pod and seed isolates. Diaporthe isolates, predominantly isolated from pods had no stroma, abundant perithecia, and ascospores with a highly variable length-to-width ratio. The two northern biotypes (Dps and Dpc) were differentiated according to mycelial texture and dark body formation in culture. Mycelial growth of the Diaporthe/Phomopsis isolates in culture was differentially affected by temperature. However, some Diaporthe and Phomopsis types from Indiana grew as well as the isolates from Alabama, Georgia, and Mississippi at 30 and 35$\sp\circ$C. Pathogenicity of Phomopsis isolates varied in seedling inoculation tests, but Diaporthe type isolates were generally more virulent. Variability among the Diaporthe/Phomopsis isolates was further corroborated by the identification of twenty different vegetative compatibility groups. The aminopeptidase activity of the isolates was higher with beta-naphthylamides of lysine, proline, and 4-methoxy-leucine; and lower with asparagine, aspartic acid, histidine, pyrrolidone and threonine. The Diaporthe/Phomopsis isolates could be readily separated from other fungal genera common to soybeans by comparing their aminopeptidase profiles through cluster analysis (Ein*Sight dendrogram). However it is not possible to get a single profile for all the Diaporthe/Phomopsis isolates or to determine the relationship between those profiles and morphological groups, since isolates within the same cluster in the dendrogram belong to different morphological groups. Hydrolytic activity of the Diaporthe/Phomopsis isolates also was modified by changes in preincubation temperature, further indicating the importance of temperature in evaluating isolate variability.
Degree
Ph.D.
Advisors
Abney, Purdue University.
Subject Area
Plant pathology|Botany
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