Rebecca Higgins

Variation in Sclerotinia sclerotiorum Bean Isolates from Multisite Resistance Screening Locations

There is no complete resistance to Sclerotinia sclerotiorum, cause of white mold in dry bean (Phaseolus vulgaris). Variable resistance expression is one problem in screening for improved white mold resistance. With no previous information in the literature, pathogen variation in multisite screening nurseries was evaluated as one cause of diverse resistance expression. In all, 10 isolates of S. sclerotiorum used in greenhouse screening and 146 isolates collected from nine white mold field screening nurseries in major bean production areas in the United States were compared using mycelial compatibility groupings (MCGs) and an aggressiveness test. These 10 greenhouse screening isolates formed six MCGs. Among 156 field and greenhouse isolates, 64 MCGs were identified and 36 of those were each composed of a single unique isolate. Significant differences in isolate aggressiveness were found between some isolates in different MCGs but the isolates within an MCG did not differ in aggressiveness. High isolate variation found within and between field locations could influence the disease phenotype of putative white mold resistant germplasm. We next compared genotype and phenotype of isolates from screening nurseries and those from producer fields. Variability found in and among screening locations did reflect variability found in the four producer fields sampled. White mold resistance screening can be improved by knowledge of isolate genotypic and phenotypic characteristics.

Description of Mesocriconema ericaceum n. sp. (Nematoda: Criconematidae) and notes on other nematode species discovered in an ericaceous heath bald community in Great Smoky Mountains National Park, USA

A new species of Mesocriconema and a unique assemblage of plant-parasitic nematodes was discovered in a heath bald atop Brushy Mountain in Great Smoky Mountains National Park. Mesocriconema ericaceum n. sp., a species with males, superficially resembles M . xenoplax . DNA barcoding with the mitochondrial COI gene provided evidence of the new species as a distinct lineage. SEM revealed significant variability in arrangement of labial submedian lobes, plates, and anterior and posterior annuli. Three other nematodes in the family Criconematidae were characterised from the heath bald. Ogma seymouri , when analysed by statistical parsimony, established connections with isolates from north-eastern Atlantic coastal and north-western Pacific coastal wet forests. Criconema loofi has a southern Gulf Coast distribution associated with boggy soils. Criconema cf. acriculum is known from northern coastal forests of California. Understanding linkages between these species and their distribution may lead to the broader development of a terrestrial soil nematode biogeography.

COMPARING MEASURING METHODS USING THE SENSITIVITY RATIO: AN APPLICATION TO RESISTANCE SCREENING IN SOYBEANS

When there are several methods of measuring a physical or chemical property, it is necessary to determine which method is best. If both methods are measured on the same scale, the most precise method will be preferred. However, often the methods have different scales. The sensitivity ratio allows for explicit comparison of methods with different scales. We use the sensitivity ratio to compare soybean resistance screening methods to evaluate the resistance of soybean varieties to Sc/erotinia sc/erotiorum. When compared to the root mean square error or the coefficient of variation, the sensitivity ratio can order methods differently both when the methods are measured on different scales and on the same scale. Our results cast doubt upon using standard precision statistics such as the root mean square error or the coefficient of variation to compare measuring methods and we suggest that the sensitivity ratio should be used instead. Conference on Applied Statistics in Agriculture Kansas State University New Prairie Press https://newprairiepress.org/agstatconference/2003/proceedings/20 238 Kansas State University