Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot.

Soil amendment with different organic materials was evaluated in greenhouse experiments for effects on root rot and growth of sugarcane. Materials included composts prepared from cotton gin trash, cottonwood bark, mixed hardwood bark, municipal solid waste, and municipal yard waste; municipal biosolids; and a sugar mill by-product, filterpress cake. Field soil, steam-treated field soil, and steam-treated soil infested with Pythium arrhenomanes were amended with nonsterile or steam-treated organic materials. A metalaxyl fungicide treatment was included for comparison. When added in nonsterile form, cotton gin trash compost, filterpress cake, and biosolids suppressed disease and increased plant growth in field soil and soil infested with P. arrhenomanes, but this ability was reduced after steam treatment. Bark composts were capable of suppressing root rot and increasing plant growth in field soil and Pythium-infested soil when added in either nonsterile or steam-treated forms. Plant growth in steam-treated soil was not promoted by nonsterile or steam-treated materials. Disease suppression provided by organic materials resulted in plant growth increases generally lower than those resulting from metalaxyl treatment in steam-treated soil infested with P. arrhenomanes, but some amendments resulted in growth increases comparable to those obtained with the metalaxyl treatment in field soil. Municipal waste composts had no effect or were detrimental to sugarcane growth. Differences in microbial community composition and chemical properties, including N content, C:N ratio, and other mineral nutrient levels, distinguished organic materials that may suppress disease and promote plant growth by different mechanisms. Microbial activity level of a material was an indicator of potential for disease suppression. The study results suggest that the severity of root rot in sugarcane may be reduced by amending soil with some organic materials.

Weeds in the Poaceae and Cyperaceae families prevalent in sugarcane fields were evaluated as potential hosts for the root rot pathogen, Pythium arrhenomanes. In greenhouse studies, bermudagrass, broadleaf signalgrass, browntop panicum, barnyardgrass, large crabgrass, goosegrass, itchgrass, johnsongrass, Italian ryegrass, and purple nutsedge became infected when grown in steam-treated soil infested with P. arrhenomanes. However, the extent of root colonization, symptom severity, and growth reductions varied among species. Symptom severity and root colonization by P. arrhenomanes were less when weeds were grown in sugarcane field soil in the greenhouse than when weeds were grown in Pythium-infested, steam-treated field soil. Levels of root colonization by P. arrhenomanes in both experiments were greatest for johnsongrass and itchgrass and lowest for browntop panicum, goosegrass, and Italian ryegrass. For weeds collected from sugarcane fields, frequencies for colonized plants were moderate to high, but the extent of root colonization by P. arrhenomanes was low for all except johnsongrass. The results indicate that weeds can serve as hosts for P. arrhenomanes and may play roles in the epidemiology of Pythium root rot on sugarcane.

Sri Lankan traditional rice germplasm (Oryza sativa indica) consists of a wide variety of morphology and days to flowering (DF). The objective of this research was to develop a mini core collection representing the DF variation of the total collection. Three hundred and eighty four rice accessions from 53 Sri Lankan traditional rice varieties were evaluated for morphological and flowering time variation. The experiment was carried at Rice Research and Development Institute, Bathalagoda, Sri Lanka during the late short day season (Maha), 2012/2013.Three hundred and forty five accessions flowered and 39 accessions did not flower during the experimental period of 210 days. Two principal component analyses (PCA) were performed and subsequently 2 dendograms were developed for flowered and not flowered accessions. Sixty eight percent of total observed variation was explained through 6 principal components (PC's) by DF and fourteen quantitative morphological characters of 345 flowered accessions. Seventy nine percent of total observed variation of not flowered 39 accessions was explained through 4 PC's by 9 quantitative morphological characters. Ninety accessions were selected from 2 dendograms for development of a mini core collection; out of which 85 accessions represented flowered accessions based on minimum and maximum DF variation in each cluster of the dendogram. Five randomly selected accessions represented each cluster of not flowered accessions. Minimum and maximum DF values of both total collection and mini core collection were 56 and 189 days, respectively. Average DF of total flowered collection and mini core collection was 79.16 ± 0.95 and 87.95 ± 3.1, respectively. A similar trend in the regression relationship between DF and plant height and, DF and leaf length of the leaf prior to flag leaf was observed in total flowered collection and mini core collection, indicating the representation of mini core collection for flowering time variation.

Phyllosphere epiphytic microorganisms of 15 Sri Lankan rice varieties were determined and 81 different recognizable taxonomic units of microbes were isolated. Three bacterial and 18 fungal isolates inhibited the growth of Magnaporthe grisea and Rizoctonia solani in vitro. Copyright © 2006 John Wiley & Sons, Ltd