Shrishail S. Navi

Disease management factors influencing yield and quality of sorghum and groundnut crop residues

Crop residues from groundnut and sorghum constitute important fodder resources for dairy production and fodder trading on the Deccan Plateau in India. This paper addresses the effect of important diseases of groundnut and sorghum on pod and grain yield and crop residue yield and quality. In four genotypes of groundnut, late leaf spot (Phaeoisasariopsis personata) and rust (Puccinia arachidis) are the two major foliar diseases that together could reduce pod and haulm yield by 70% and in vitro digestibility of haulms by 22%. Two genotypes (ICGV 9202 and 92093) were highly resistant to these foliar diseases maintaining high pod and haulm yield as well as high in vitro digestibility of haulms (>62.3%) even under highest disease pressure. Important diseases in sorghum investigated were a viral disease caused by maize stripe virus (MStV) and anthracnose caused by Colletotrichum graminicola. MStV reduced grain yield by 30%, stover yield by 42% and digestible stover yield by 45%. Effects of MStV were highly genotype-dependent and grain and stover were affected in different ways in different varieties. The choice of appropriate genotype for a given farming situation will depend on trade-off scenarios for benefits from grain and stover. Similarly, anthracnose could reduce grain yield by 47% and stover yield by 23% but effects on stover quality were variable. As observed for MStV, effects of anthracnose were highly genotype-dependent and genotypes were identified that maintained high grain and stover yield under high disease pressure.

Effect of temperature and humidity regimes on grain mold sporulation and seed quality in sorghum (Sorghum bicolor (L.) Moench)

Abstract Grain mold, induced by a number of non-specific fungi, causes substantial loss to seed/grain yield and quality in sorghum (Sorghum bicolor (L.) Moench). Fungal sporulation and grain mold severity are greatly influenced by temperature and relative humidity (RH) levels. We studied the effects of three incubation temperatures (25, 27 and 28°C) and two sets of RH levels (first set: 85, 90, 95, 98, and 100%, second set: 95, 96, 97, 98, 99 and 100%) on sporulation and grain mold severity in three major mold fungi (Curvularia lunata, Fusarium moniliforme, and Bipolaris australiensis) and on four each of resistant, moderately resistant and susceptible sorghum genotypes for sporulation and mold severity of major fungi. Results indicated that both fungal sporulation and grain mold severity increased on most sorghum genotypes with increasing incubation temperature from 25 – 28°C and RH levels from 95 – 98%. A linear relationship was observed among RH levels, grain mold severity and fungal sporulation. The highest sporulation of all the three fungi occurred at 28°C and 98% RH after 5 days of incubation. Among the three fungi, C. lunata grew and sporulated faster than B. australiensis and F. moniliforme, in that order. Among the sorghum genotypes, IS 25017 supported the least sporulation and had the lowest mold severity, followed by IS 8545 and PVK 801. Seed quality parameters, such as seed germination, seedling vigor index, field emergence potential, dehydrogenase and ά-amylase activities declined significantly with increasing temperature and RH levels that supported heavy sporulation and grain colonization.

Fungi Associated with Sorghum Grains in Rural Indian Storages

ABSTRACT A total of 67 sorghum grain samples were chosen from a survey in 1997; 34 samples from the 1996 rainy season and 33 from the 1996/97 post rainy season harvests. Five kilograms of sorghum grains were collected from each of the grain lots stored in jute bags, mud-lined baskets, metallic containers, polypropylene bags, and grains piled in a corner of a room. At ICRISAT, each sample was evaluated for fungi associated with sorghum grain and grain germination in a representative sample of 200 grains per treatment: (i) grains surface-sterilized in 1% sodium hypochlorite (NaOCl) prepared from Clorox(r), and not treated with fungicide benomyl, (ii) grains surface sterilized and treated with benomyl (0.05%), (iii) grains not surface sterilized but treated with benomyl and (iv) grains neither surface sterilized nor treated with benomyl. Major fungi with a mean frequency of > 5% across storages, cultivars, harvesting seasons and treatments were: Alternaria alternata, Aspergillus flavus, A. niger, Bipolaris australiensis, Curvularia lunata, C. lunata var aeria, Fusarium verticillioides, Penicillium citrinum, Phoma sorghina, and Rhizopus stolonifer. In addition, 41 fungi with a mean frequency of < 5% across storages, cultivars, harvesting seasons and treatments were observed. Significant differences were observed in grain germination and fungal frequency of rainy and post rainy season samples, storages and cultivars. Majority of the rabi samples represented improved variety Maldandi and stored their grain in jute bags, while kharif samples represented much wider varieties and hybrids and storage techniques. This study may help better understand danger of contamination by mycotoxins in relation to the mycoflora associated with sorghum grains.

Host plant resistance to grain mould in germplasm accessions of pearl millet (Pennisetum glaucum [L.] R. Br.)

Abstract The paucity of information on the moulds in Indian pearl millet (Pennisetum glaucum) led to the studies that were conducted at ICRISAT, India to evaluate (a) 447 germplasm accessions of 32 countries for mould reaction in rainy season, (b) threshed grain mould rating (TGMS) and mycoflora on grains of each accession, and (c) mould scores in field and in vitro. Post physiological maturity evaluation showed that 16% of the accessions secured a mould rating of 2. In TGMS, 18% were mould free and 57% secured a rating of 2 on a 1 – 9 scale. Assessment of twenty representative accessions in vitro against individual and mixed conidial suspensions (1 × 10(6) conidia ml(−1)) of Fusarium moniliforme, F. pallidoroseum and Curvularia pennisetti indicated significant correlation (r = 0.97) between the overall field and in vitro scores of mixed spores inoculations. The mycoflora for TGMS in blotter test revealed that Fusarium moniliforme, F. pallidoroseum, Curvularia pennisetti, Helminthosporium spp., Alternaria spp. and Colletotrichum spp. to be the major fungi affecting pearl millet grain. It is advisable to harvest panicles at the physiological maturity stage to obtain better quality grains. A strong negative correlation between TGMS and % GS (r = 0.4601) and positive correlation between TGMS and % UGS (r = 0.4654) indicated that, the lesser the threshed grain mould rating higher the % seed germination.

Prevalence of major foliar and panicle diseases of Sorghum (Sorghum bicolor [L.] Moench) in the Deccan plateau of India

Abstract 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.

Effects of colonisation by different strains of Coniothyrium minitans on the viability of sclerotia of Sclerotinia sclerotiorum

White mold is a major disease in commercial soybean production. An effective measure to reduce the negative effects of Sclerotinia sclerotiorum is the use of bio-fungicides. Strains of Coniothyrium minitans were isolated and efficacy tests against S. sclerotiorum was studied. The efficacy of pycnidiospores sprays of strain N09 (GenBank Accession No HQ908274) from Iowa, USA and strain CON/M/91-08 of Contans® WG were compared in a series of experiments. Sclerotia viability was significantly (P < 0.05) lower in both sclerotia-infested-sterilized-soils (SISS) and sclerotia-infested-unsterilized-soils (SIUS) sprayed with N09 compared with CON/M/91-08 and control at 3°C for 75d and 90d sampling. Similarly, sclerotia viability was significantly (P < 0.05) lower at 23°C for 45, 60 and 75d sampling in SISS and 45, 75 and 90 d sampling in SIUS compared with CON/M/91-08 and control. In contrast, viability of N09 colonies were significantly (P < 0.05) higher than that of CON/M/91-08 both at 3°C and 23°C in SISS across sampling periods. While in SIUS, N09 colonies were significantly higher at 3°C for 15, 30, 45, 75 and 90 d sampling, and at 23°C for 30, 60 and 75 d sampling. Also, (1) N09 had a faster growth rate and produced 1.5 times more pycnidiospores than CON/M/91-08; (2) mycoparasitism by N09 was faster than CON/M/91-08; and (3) co-inoculation of sclerotia and the strains, N09 showed lower sclerotia reproduction than CON/M/91-08. Our data suggest that the new strain N09 has a greater efficiency than CON/M/91-08 in killing sclerotia.