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DNA analysis of agriculturally important fungi using polymerase chain reaction (PCR)-based methods is becoming routine in research and for diagnostic purposes. Rapid, small-scale DNA isolation methods that take advantage of the sensitivity, speed and automation potential of PCR technology are needed for timely analysis of important plant pathogens. DNA isolated from Claviceps africana (causal agent of ergot of sorghum) using several standard DNA extraction protocols was found to be unamplifiable using PCR. The standard methods apparently failed to separate DNA from substances inhibitory to the Taq polymerase enzyme. We obtained DNA amenable to PCR analysis using a novel method involving magnetic beads and high salt extraction buffer. The biomagnetic purification method allowed us to obtain reliable PCR amplification of the internal transcribed spacer (ITS) regions of rDNA of Claviceps africana, making genetic comparisons possible.

Extensive on-farm disease surveys were conducted from August 1999 until March 2001 in four sorghum-growing states of the Indian Deccan plateau. A total of 965 fields were surveyed covering 228 fields in Andhra Pradesh (AP), 406 in Karnataka (KAR), 290 in Maharashtra (MH) and 41 in Tamil Nadu (TN). Among 14 foliar diseases observed, maize stripe virus (MStV), a tenuivirus transmitted by the delphacid plant hopper (Peregrinus maidis), and among five panicle diseases, ergot or sugary disease (Claviceps sorghi and C. africana) were the most destructive diseases. MStV was prevalent in 28.4% and ergot in 13.4% of the fields surveyed in two years across four states. Yet, the mean incidence of MStV in AP was 6% with 85% mean severity. The values in KAR were 12% incidence and 83% severity, in MH 5% and 67%, and in TN 12% and 76%, respectively. The mean incidence of ergot in AP was 34% with 67% mean severity. The values in KAR were 41% and 79%, in MH, 30% and 67%, and in TN 100% and 100%, respectively. Variation in frequency of occurrence of MStV was observed between 1999 and 2001. Variations in frequency could be due to weather factors, vector survival, cropping pattern, and host specificity. The frequency of ergot also was varying among years, locations, seasons and cultivars. An ergot epidemic was observed during the 1999 rainy season in Maachinenipalli village (16°35′N; 78°3′E), Andhra Pradesh. In September 2000, the disease had spread to 13 neighboring administrative zones damaging about 130,000 ha. This paper elucidates the distribution of diseases observed between 1999 and 2001 but does not imply that the diseases are restricted necessarily to a particular zone or location. [ABSTRACT FROM AUTHOR]

Twenty graminaceous plant species were evaluated for their susceptibility to the two sorghum ergot pathogensClaviceps sorghiandClaviceps africana. Five species viz.,Sorghum arundinaceum,Sorghum halepense,Sorghum versicolor,Sorghum virgatumandPennisetum glaucumwere found to become infected by both pathogens via inoculation with 106 conidia/ml. Species which did not become infected under these conditions includedPennisetum pedicellatum,Zea mays, and species ofPanicum,Brachiaria,Cenchrus,Andropogon,Dichanthium,Chrysopogon,Iseilema,BothriochloaandChloris.Honeydew secretions were observed from infected flowers of susceptible plant species. There was marked variation in size of macroconidia of bothC. sorghiandC. africanaon different hosts on which the pathogens were able to establish symptoms. Dimorphism was observed for macroconidia produced onP. glaucum, as elliptical and spindle shaped macroconidia were observed. Based on inoculation under greenhouse conditions, we conclude thatC. sorghiandC. africanamay have similar host ranges. [ABSTRACT FROM AUTHOR]

High molecular weight DNA of Phytophthora infestans was extracted using a modification of the commercial QIAGEN column procedure. Both a 'maxi' and `mini' procedure are described. The maxi procedure utilizes a QEAGEN-tip 500 column while the mini procedure utilizes a QIAGEN-tip 20 column. When fungal protoplasts were used as starting material from 9 g (fresh weight) of mycelium. nearly 500 pg of DNA in the size range of 20- 200 kb was obtained and the product was successfully used in construction of a lambda genomic library. The modified QIAGEN method can replace the more time- consuming, and expensive cesium chloride density gradient centrifugation for extraction of ultra-pure DNA from P. infestans. [ABSTRACT FROM AUTHOR]