Stalk Rots

Stalk rots of sorghum are diseases of great destructive potential Rots caused by the fungi Macrophomina phaseolina and Fusarium moniliforme appear to be widely distributed stalk diseases of sorghum. Recently a vascular pathogen, Acremonium strictum that causes leaf and stalk death, has become important on sorghum. Improved high-yielding varieties tend to be highly susceptible to these diseases. Losses vary from season to season and region to region. Grain losses exceeding 15% are not uncommon; as much as 60% can occur. Several fungi and bacteria are often associated in diseased roots and stalks, suggesting that stalk rot diseases are of complex etiology. Etiology and host resistance to charcoal rot, fusarium root and stalk rot, and acremonium wilt are discussed

Variation in Phenol Content of Sorghum Lines after Inoculation with Colletotrichum graminicola

Phenolic compounds accumulate in numerous plant species following infection by plant pathogens (Kuk 1972). Many of such compounds, or their oxidation products are toxic to pathogenic and non-pathogenic fungi, and have been considered an important factor in induced resistance to plant pathogens. The variation in phenol content following infection with Colletotrichum graminicola, the causal fungus of anthracnose of sorghum was studied using six sorghum lines, resistant (A 2267-2, IRAT204); moderately resistant (IS 3758, IS 8354); and susceptible (IS 3089, IS 18442) to anthracnose. The lines were selected based on their disease reactions in the International Sorghum Anthracnose Virulence Nursery conducted at 10-12 locations in India and Africa during 1992 and 1993. Plants of each genotype were grown in 13-cm square plastic pots in a Vertisol mix (Vertisol, farmyard manure, and sand, 2:1:1 by volume, steam sterilized at 105°C) in a greenhouse at ICRISAT-Patancheru

A greenhouse screening technique to assess rust resistance in sorghum

Studies were conducted to determine the influence of plant growth stage, inoculum density, temperature, and relative humidity (RH) on development of rust (Puccinia pupurea) in sorghum (Sorghum bicolor). Rust development was maximum (>80% severity), when plants of a susceptible sorghum genotype (IS 18420) were inoculated at the four‐ to five‐leaf stage with an inoculum concentration of 4 × 106 urediniospores per ml and incubated at 20–25°C under high RH (>90%) for 24 h. Disease severity (percentage leaf area covered with rust pustules) scores were taken 2 weeks after inoculation. Using this technique, 29 sorghum genotypes were screened for rust resistance in a greenhouse. This technique proved effective In discerning resistant and susceptible genotypes, and IS 3979, ICSH 110, ICSH 86647 and ICSH 871035 were identified resistant (<20% rust severity) compared with a susceptible control IS 18420 (90% rust severity). This technique is simple and rapid, and can be used effectively and economically to screen, on a large scale, germplasm lines and breeding populations in the greenhouse

Effects of Host Resistance, Temperature, and Duration of Wetness of Leaf Blight Development of Grain Sorghum

The effects of post-inoculation temperatures and periods of leaf wetness of leaf blight (Exserohilum turcicum (Pass.) Leonard and Suggs) development were studied in three sorghum genotypes (IS 3443C-40, ICSV 1, and 296B or Local FSRP) having varying levels of blight resistance. In two different experiments, pot-grown plants of these genotypes were spray-inoculated and subjected separately to i) six temperature regimes (10,15,20,25,30 and 35°C) for 24h with a 12h photoperiod and high relative humidity (100% RH) and ii) six periods of leaf wetness (RH-100%) of 2,4,6,8,24, and 48 h at 25°C Leaf blight severity (percentage leaf area damaged) was maximum (55%) at 25°C at 24 h of leaf wetness period in the susceptible genotypes Local FSRP and 296B. There was no leaf blight development at 10°C and 35°C and, significnatly, only low blight development (%) up to 8 h of leaf wetness. Implication of these findings in refining leaf blight screening technique is discussed

Influence of soil moisture stress and Macrophomina phaseolina in charcoal rot development in grain sorghum

The effects of Macrophomina phaseolina, soil moisture stress (SMS), and their interaction on charcoal rot development in sorghum were studied in field experiments. Individual effects of the pathogen and that of SMS were studied by eliminating SMS by furrow irrigation, and the pathogen by soil fumigation with methyl bromide, respectively. Significant effects of the pathogen, SMS, and pathogen x SMS interaction were found on charcoal rot development (percentage lodging) in sorghum hybrid CSH 6. Soil fumigation drastically reduced the population of the pathogen. Lodging was 3.18% in no-SMS plots as against 100% in the SMS plots. Under SMS, lodging was 6.27% in the fumigated plots compared with 100% in the non-fumigated plots, indicating that moisture stress alone cannot cause significant lodging in the absence of the pathogen. There was no colonization of stalks by the pathogen in the fumigated SMS plots compared with very high colonization in the non-fumigated SMS plots. Grain yield reduction due to charcoal rot was estimated between 20 and 33%

Effect of moisture stress, plant population density and pathogen inoculation on charcoal stalk rot of sorghum

The effects of moisture deficit stress, plant population density and pathogen inoculation technique on charcoal stalk rot in the sorghum hybrid CSH 6 were studied in the 1980–81 and 1981–82 post-rainy seasons at three locations in India. Incidence and severity of charcoal rot caused by Macrophomina phaseolina were compared in three plant population densities, subjected to different moisture stress regimes created by withholding irrigation at various plant growth stages. Natural infections were compared to artificial inoculation with M. phaseolina. Combinations of moisture stress, plant population and inoculation treatments were compared to identify the combination most likely to develop maximum disease. Lodging, the first external symptom of charcoal rot, was significantly correlated with other disease symptoms used to measure charcoal rot, such as soft stalk, number of nodes crossed by M. phaseolina infection, root damage and plant senescence. In both seasons the highest incidence of lodging occurred when moisture stress was induced at the ‘flag leaf visible in the whorl’ growth stage. The greatest incidence of the disease was recorded in the highest plant population (266 700 plant ha-) at all three locations. No significant differences were found between artificially and naturally inoculated treatments. The maximum number of lodged plants was found at a density of 266 700 plants ha-1 when moisture stress was induced at the ‘flag leaf visible in the whorl’ growth stage

Etiology of stalk rot and lodging in grain sorghum

The effects of fungi alone, dmught-stres* alone, and in combination on the development of stalk rot (%lodging)Sorghum were studied in field experiments at ICRISAT Asia Center, Patancheru and at University of Agricultural Sciences, Dharwad in india. Stalk rot and lodging occurred In drought-stressed................

Incidence of charcoal rot in sorghum cultivars as affected by sowing date and plant density

The effects of sowing dates and plant densities on charcoal rot development in sorghum cultivars grown under recedingsoil moisture and natural infection conditions were studied during two postrainy seasons at four locations in India. In both the seasons, maximum charcoal rot infection (as measured by lodging) occurred in the first sowing. Significant (P <0.05) differences were recorded in charcoal rot incidence among the test cultivars, and E 36-1 from Ethiopia was resistant at all locations. High incidence of lodging was recorded even in a population of 133,350 plants ha -1 and this plant density was found to be adquate to quantify genotypic differences in lodging. Lodging was significantly (P < 0.05) correlated with soft stalk, number of nodes crossed, root damage and plant senescence

Seedborne infection of Eleusine coracana by Bipolaris nodulosa and Pyricularia grisea in Uganda and Kenya

Seed samples of finger millet (Eleusine coracana) collected from Uganda and Kenya had mixed infections with Bipolaris nodulosa (4-49%) and Pyricularia grisea (7-55%). Most samples showed poor germination and were unfit for sowing because of a high percentage of Seedborne infection. We obtained similar seed infection counts with the standard blotter, deep-freezing blotter, and agar plate methods, which suggests that any of these methods could be used for routine seed health testing. However, sporulation was better on frozen seeds. Gray or black discolored seeds had higher levels of infection by P. grisea than apparently healthy, normal reddish brown seeds. Plating of seed components showed that both fungi were present in the pericarp and endosperm but not in the embryo. Seed transmission tests demonstrated the ability of these fungi to kill young seedlings

Effects of nitrogen, plant density, moisture stress and artificial inoculation with macrophomina phaseohna on charcoal rot incidence in grain sorghum

Effects of different levels of nitrogen, plant density, soil moisture stress and of anificial inoculation with Macrophomina phaseolina on charcoal rot incidence in grain sorghum were studied in a split-split-split field plot design. Nitrogen levels were applied to main plots; plant densities, moisture stresses and inoculations were replicated in sub, sub-sub and sub-sub-sub plots. A gradient of soil moisture stress was created during grain filling by line-source sprinkler irrigation. Analysis of variance indicated significant effects of moisture stress, plant density and their interactions on charcoal rot disease incidence as measured by piant lodging. Lodging increased linearly along the gradient of water supply suggesting a positive relationship between moisture stress and disease development. Lodging was also significantly (P < 0.01) and highly correlated with other charcoal rot disease parameters (soft stalk, number of nodes crossed, root infection and plant senescence). There were no significant differences (P < 0.05) in charcoal rot incidence among inoculation treatments. Lodging increased in both high nitrogen and high plant population treatments under moisture stress condition