Article

Screening for Ergot Resistance in Sorghum

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Abstract

Experiments were conducted at Arsi Negele, Ethiopia, during the 1988 and 1989 rainy seasons to determine a suitable combination of sorghum panicle trimming (a method used to remove pollinated spikelets), inoculation, and bagging to develop an ergot resistance screening technique. Results showed that the most suitable method was a single inoculation of nontrimmed panicles when anthesis began in a panicle, followed by bagging. Comparison of resistance evaluation methods suggested that susceptible genotypes could be identified by a simple and rapid visual ergot rating on a 1-5 scale, where 1 = no ergot and 5 = more than 50% spikelets in a panicle infected. However, resistance of genotypes should be confirmed by counting infected and healthy spikelets in a few primary branches of panicles. Screening of 213 Ethiopian sorghum accessions led to the identification of six ergot-resistant lines—ETS 1446, 2448, 2465, 3135, 4457, and 4927—that are well adapted to the highlands of Ethiopia.

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... Disease evaluation techniques and artificial inoculation techniques have been developed to screen germplasm for resistance to sugary disease in the field and greenhouse (Sundaram, 1970, 1971; Khadke et al., 1978; McLaren, 1992; Musabyimana et al., 1995). Tegegne et al. (1994) evaluated inoculation techniques and compared quantitative and visual assessment methods to screen germplasm for resistance to sugary disease. Quantitative assessment required counting the number of spikelets with sphacelia, with healthy grain, and without either, in a composite sample of spikelets from one primary branch of each node of the panicle rachis. ...
... At least 20 panicles were observed in each plot for presence or absence of the disease and percentage disease incidence was calculated. The second rating was based on a 1±5 scale (Tegegne et al., 1994) and represents severity of sugary disease within a representative sample of the plot as follows: 1, no infected florets on the panicle; 2, 1±10 infected florets on the panicle; 3, 11±25 infected florets on the panicle; 4, 26± 50 infected florets on the panicle; 5, . 50 infected florets on the panicle. ...
Article
Ergot or sugary disease of sorghum has become an important constraint in North and South American countries that rely on F1 hybrid seeds for high productivity. The objective of this research was to determine the vulnerability of various germplasm sources and publicly bred sorghum lines to sugary disease (Claviceps africana) in the United States. Flower characteristics associated with sugary disease resistance were also studied. A-/B-line pairs, R-lines, putative sources of resistance and their hybrid combinations with an A3 cytoplasmic male-sterile source were evaluated using a disease incidence, severity, and dual-ranking system. Trials were planted in a randomized complete block design with three replications and repeated in at least two planting dates. Planting dates and pedigrees had significant effects on overall ranking for resistance. A-lines were most susceptible to sugary disease. R-lines were more susceptible than B-lines with respect to incidence and severity of the disease. Newer releases of A- and B-lines were more susceptible to sugary disease than older releases. Sugary disease reaction of A-lines was a good indicator of disease reaction of B-lines. Tx2737, a popular R-line, was highly susceptible to sugary disease in spite of being a good pollen shedder because the stigma emerged from glumes 2–3 days before anthesis. The combination of flower characteristics associated with resistance were least exposure time of stigma to inoculum before pollination, rapid stigma drying after pollination, and small stigma. An Ethiopian male-fertile germplasm accession, IS 8525, had good levels of resistance. Its A3 male-sterile hybrid had the highest level of resistance in the male-sterile background. IS 8525 should be exploited in host-plant resistance strategies.
... ) inoculum concentrations in greenhouse assays (Frederickson et al., 1994; Tegegne et al., 1994; Reed et al., 2002) or variable concentrations in field infections (Dahlberg et al., 2001). Selection for partial resistance using high inoculum concentrations could lead to a 'cryptic error' in resistance testing, where lines that may have some resistance are rejected in high-disease environments (Zadoks & Schein, 1979). ...
Article
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... Our findings indicate that a concentration of 10 6 conidia/mL was optimum for infection of the male sterile line used in this study, and that higher concentrations did not result in significantly higher infection levels. Conidial concentrations of ~10 6 conidia/mL were used by Tegegne et al. (1994), Musabyimana et al. (1995) and Reed et al. (2002) in their studies to identify resistant germplasm of Sorghum and other grass genera to C. africana. Workneh and Rush (2006) considered that the use of conidial concentrations of 10 5 and 10 6 conidia/mL in their predictive model may result in an overestimation of ergot severity. ...
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Chapter
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Interaction of plants with environmental factors and microbial world is a dynamic process. As part of this ever-changing process new disease emerges or minor disease may become major with time. This chapter presents a very brief account of well-studied old diseases of sorghum and emphasizes on emerging diseases with particular reference to India. Description of sorghum diseases caused by fungi, bacteria, and their transmission through seed implies quarantine significance. Thus, awareness about the quarantine pests of different countries is essential for facilitation of smooth germplasm exchange. Diseases distribution, losses, symptomatology, and management options have been discussed in detail. In this chapter, we have generated environmental (ecological) niche model for the pathogens causing sorghum diseases due to fluctuations in environment caused by climate change. Ecological Niche Model using Maxent is a class of method that uses occurrence data in conjunction with environmental parameters to make a correlative model of the environmental conditions that meet pathogens’ ecological requirements and predicts the relative suitability of habitat.
Chapter
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Article
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Article
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Ergot (caused predominantly by Claviceps africana Freder., Mantle & De Milliano) is a disease of sorghum (Sorghum bicolor L. Moench), with pollen traits reported to be associated with resistance. This study investigated the genetic architecture and the role of pollen quantity (PQ) and pollen viability (PV) in ergot resistance in an F5 recombinant inbred line (RIL) sorghum population developed from the cross between an elite germplasm line, 31945-2-2 from Australia, and a recently reported putatively resistance source line, IS8525. Percentage ergot infection (PCERGOT) in IS8525 was very low, while in contrast, 31945-2-2 was heavily infected at all inoculation dates of the two field trials conducted under artificial epiphytotic conditions during 2001 and 2002. The distribution of the predicted means for PCERGOT, PQ, and PV was normal, suggesting that the traits are polygenic in nature. Genetic correlations between the two pollen traits and PCERGOT were moderately negative, indicating that there might be some common genetic factors controlling these traits. However, low R-2 values of PQ (11%) and PV (9%) suggest that only a small part of the total variability in ergot resistance in this population was due to the variability in PQ and PV Correlations between ergot scores for different sampling dates (SDATEs) and years were moderate to high, indicating relatively low levels of genotype x environment interaction. Genetic variance and broad sense heritability were also high, indicating that ergot resistance is likely to respond well to conventional selection.
Article
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Forty Chinese sorghum landraces maintained by the USDA-ARS Plant Genetic Resources Conservation Unit, Griffin, GA were evaluated for ergot resistance at the Texas A&M Research Farm, College Station, Texas, during the 2005 and 2006 growing seasons. The male sterile line, ATx623, was included as a susceptible control and three IS8525 derived lines were included as resistant controls. The disease infection level was low in the susceptible check in 2005 due to unfavorable environmental conditions, but the majority of the Chinese accessions showed a higher level of tolerance than the resistant controls and in contrast, infection severity was high in 2006. The IS8525 resistant controls averaged 25% infection compared to an average infection of 18% for the 40 Chinese accessions. Four Chinese accessions, PI63923, PI511832, PI610749, and PI610688, recorded less than 10% ergot infection and thus, these four accessions may possess genes for ergot resistance. Further research is underway to evaluate these accessions under multi-environments to confirm resistance and to determine if the resistance is associated with pollination characteristics. Accepted for publication 19 February 2008. Published 19 May 2008.
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