THE AMERICAN PHYTOPATHOLOGICAL SOCIETY

Abstract

EFFECT OF TEMPERATURE AND MICROWAVE IRRADIATION ON THE VIABILITY tobacco cells undergoing the hypersensitive reaction to PseuAND MOISTURE CONTENT OF SCLEROTIA OF SCLEROTIUM ROLFSII. M. A. domonas pisi. Within 90 min after inoculation, tobacco cells Acra, S. F. Jenkins and E. Echandi. Dept. of Plant Pathology, exhibited an increased efflux of K+ and a net uptake of H+. North Carolina State University, Raleigh 27650. At pH 6.0 maximum fluxes of approximately 10 Umole K+ and 3.8 pmole H+/g (fresh weight) tobacco cells/h occurred between 2.5 Sclerotia of one isolate of S. rolfsii produced on oat grains in and 3 h after inoculation. K+ uptake rates declined concurnon-sterilized field soil were dried in incubators at various rently from about 1.0 to 0.1 pmole/g/h. K+ efflux from tobacco temperatures (20-50C) for either 2 or 4 days. Germination was cells was highly dependent upon H+ uptake capacity: high exterdetermined on non-sterile soil using a 1% methanol assay. Both nal pH or the proton ionophore FCCP reduced efflux rates subpercent germination and fresh weight were decreased with an instantially while low external pH increased efflux rates. K+ crease in temperature and time of incubation. Treatment of efflux rates were only slightly reduced by high external K+ sclerotia with microwaves (2450 MHz) reduced the percent germiconcentrations indicating that K+ efflux was not entirely nation; this reduction was enhanced as the microwave power setpassive. These results suggest the hypersensitive reaction tings (10-100% of maximum power) or irradiation time (10-160 proceeds through the activation of a K+/H+ exchange mechanism sec) were increased. When scarified sclerotia (shaken with sand across the plasmalemma. for 45 min) were irradiated, they were contaminated with microorganisms to a greater extent than non-scarified sclerotia, and their germination on field soil was inhibited. There were no differences in fresh weight among the various microwave treatUNHARVESTED PEANUT PODS PROVIDE INOCULUM OF RHIZOCTONIA SOLANI. ments, indicating that the irradiation did not affect viability D.K. Bell and D. R. Susner, Coastal Plain Experiment Station, of sclerotia by altering moisture content. Tif ton, Georgia 31793. Intact peanut pods were collected in February from a field harvested the previous September. Five cm deep layers of pods INFECTION OF GRAIN SORGHUM BY MAIZE DWARF MOSAIC VIRUS STRAIN B, were placed at 0-5, 5-10 and 10-15 cm depths in 23 x 24 cm J. D. Alexander and R. W. Toler, Department of Plant Sciences pots of heat treated (60 C, 30 min) soil and planted to Funks Texas A&M University, College Station, TX 77843. G-4507 corn and Bragg soybean. Plants were harvested after 4 weeks, and rated for root-hypocotyl disease index (RHDI, min Twenty-seven cultivars of grain sorghum were tested for sus1-max 5). Isolations were made from lesions and anastomosis ceptibility to infection by maize dwarf mosaic virus strain B group (AG) of Rhizoctonia solani was identified. The RHDI (MDMV-B) by mechanical inoculation in the field and greenhouse. averaged 2.0, 2.3 and 2.3 for corn from treatments with pods Eleven cultivars were determined by symptomology and seroat the three respective depths, and for soybean the RHDI averlogical testing to be susceptible to MDMV-B infection. These aged 1.9, 3.4 and 2.6. The RHDI values for corn and soybean cultivars were also susceptible to infection by MDMV-A. RTx430, with pods at the 0-5 cm depth were not significantly (P=0.05) SA394 and (ATx623 x RTx430) developed severe redleaf symptoms greater than the controls (1.3 and 1.5). The two remaining and many of the infected plants were killed by MDMV-B infection. RHDI values for corn and soybean were greater than the Symptoms of MDMV-B infection in the Rio cultivar were less controls. Sixty-seven and 47 isolates of R. solani AG-4 were severe than the redleaf symptoms caused by MDMV-A infection, isolated, respectively, from corn roots and soybean roots plus MDMV-B symptoms in SC0175-14E, BTx623, Hegari (8165426), hypocotyls. No other AG were isolated. RTAM 428, SA 707B, RTx09 and RTx412 were approximately equal to or slightly worse than symptoms caused by MDMV-A infection. MDMV-B infected fewer accessions but in general was more severe on the plants it infected than MDMV-A. SOYBEAN RESISTANCE TO ROOT-KNOT NEMATODE, MELOIDOGYNE INCOGNITA WARTELLEI GOLDEN AND BIRCHFIELD. W. Birchfield & B. G. Harville, Dept. Plant Path. & Crop Physiol., La. State Univ. Agric. Expt. Sta., USDA, ARS, and Dept. Agron., La. State Univ. Agric. Expt. LIQUID MEDIA FOR OOSPORE PRODUCTION BY PYTHIUM ULTIMUM. Teresa Sta., Baton Rouge, LA 70803. Arroyo and L.F. Johnson. Instituto Tecnologico de Costa Rica, San Carlos, Costa Rica, C.A., and Dept. of Entomology and Plant Wartell's root-knot nematode is a destructive soybean parasite, Pathology, Univ. of Tennessee, Knoxville, TN 37901 U.S.A., resp. but knowledge on its differential effects on soybean varieties is limited. Twenty-eight soybean varieties/ascessions, were Oospore production was determined in 5 liquid media in petri dish ieldmeted fresistanc.beance wasmesured b ema cultre.A 6mm gardiskof . utimm fom aPDAculurewas field tested for resistance. Resistance was measured by nemaculture. A 6-mm agar disk of P. ultimu fro a PDA culture was tode population build-up, and top and root host symptoms. Lowplaced in each dish containing 15-20 ml of media. Dishes were incubated in the dark at 17 C. At intervals of 7, 15, 22, and est nematode populations occurred on LA 78-17717, Braxton and in0ubays, mostno the darkiaqu17iC.d t in per s was 7,r15,m 2 ad bLA 74-4656. Less chlorosis and necrosis of foliage and stems 30 d ost f the liquid in sample dishe a removed y pipetting and decanting, and numbers of oospores were determined were observed on LA 75-1794, LA 75-1799, LA 77-10797, LA 77microscopically. Oospores were produced in largest numbers in a 10799, Braxton, Centennial, and Bragg. Lowest root galling ocminerals-lecithin-oil (MLO) medium (813 oospores/mm2) after 30 curred on LA 75-1794, LA 75-1799, LA 78-17738, Centennial, Bragg, days. In comparison, oospores produced in corn meal (10 g/L), LA 74-3854, and LA 77-10799. The most resistant varieties for oat meal (35 g/L), V-8 cholesterol (Phytopath. 65:1094), and grower trials are Bragg, Braxton, Centennial, and Forest. Davis Kentucky bluegrass (Phytopath. 72:232) were 525, 404, 256, and and Mack soybean varieties were high susceptible to the nematode. 90/mm 2 , resp. MLO medium contained (per L) 2 g NaNO 3 , 1 g K2 HPO4, 0.5 g MgSO4-7H20, 0.5 g KCI, D0 mg FeS04 and 2.5 ml lecithin in soybean oil (U.S. Biochemical Corp., Cleveland, OH). Refined lecithin powder or soybean oil was not as effective for AMINOPEPTIDASE PROFILES OF XANTHOMONAS CAMPESTRIS PV. PRUNI. oospore production as was the unextracted lecithin in soybeanoil. J. A. Bohac, A. J. Latham, and R. M. Cody. Ala. Agri. Exp. Stn., Auburn University, AL 36849. AThe profiles of aminopeptidase activity were determined for 14 K+ AND H+ TRANSPORT DURING THE HYPERSENSITIVE REACTION. M. M. isolates of Xanthomonas campestris pv. pruni. These profiles Atkinson and J. S. Huang, Dept. of Plant Pathology, North represent the quantitative hydrolysis of 15 aminoacyl-s-napthCarolina State University, Raleigh, N. C. 27650. ylamide substrates by the aminopeptidase enzyme. Activity was K+ (86 Rb) and H+ transport was studied in suspension cultured assayed by fluorescence released upon hydrolysis of substrate