Friendly microbes help rice to grow and suppress its pathogens: Trichoderma and Bacillus Vs Xanthomonas in rice

Use of biological control for the management of diseases has gained huge awareness and importance in the present situation of climate change and food residues. Biocontrol agents play interesting role in developing plant health and provide protection against biotic and abiotic stresses. In this study, we isolated Trichoderma and Bacillus sp. isolated from soil samples collected from rice fields in Kharif 2019. Profiling based on the pH of the soil, the fungal bioagents were more present in slightly acidic to neutral pH (5.8-7.2) whereas bacterial bioagents in slightly neutral to basic (7.4-8.3). The isolates were screened for their ability to produce phytohormones, cell-wall degrading enzyme and biofilm. Based on biochemical screening two Trichoderma isolates (T6 and T7) and two Bacillus isolates (B1and B5) were subjected to glasshouse studies. Per cent diseased leaf area and lesion length of plants treated with B1 were found to be effective against pathogen. However, the plant growth promotion was more enhanced by T6. Scanning electron microscopy and molecular characterisation along with their phylogenetic analysis proved the identity of isolate B1 as Bacillus subtilis and T6 as Trichoderma atroviride.

Field Characterization of Partial Resistance to Gray Leaf Spot in Elite Maize Germplasm

Forty-eight inbred lines of maize with varying levels of resistance to gray leaf spot (GLS) were artificially inoculated with Cercospora zeina and evaluated to characterize partial disease resistance in maize under field conditions from 2012 to 2014 across 12 environments in western Kenya. Eight measures of disease epidemic—that is, final percent diseased leaf area (FPDLA), standardized area under the disease progress curve (SAUDPC), weighted mean absolute rate of disease increase (ρ), disease severity scale (CDSG), percent diseased leaf area at the inflection point (PDLAIP), SAUDPC at the inflection point (SAUDPCIP), time from inoculation to transition of disease progress from the increasing to the decreasing phase of epidemic increase (TIP), and latent period (LP)—were examined. Inbred lines significantly (P < 0.05) affected all measures of disease epidemic except ρ. However, the proportion of the variation attributed to the analysis of variance model was most strongly associated with SAUDPC (R2 = 89.4%). Inbred lines were also most consistently ranked for disease resistance based on SAUDPC. Although SAUDPC was deemed the most useful variable for quantifying partial resistance in the test genotypes, the proportion of the variation in SAUDPC in each plot was most strongly (R2 = 93.9%) explained by disease ratings taken between the VT and R4 stages of plant development. Individual disease ratings at the R4 stage of plant development were nearly as effective as SAUDPC in discerning the differential reaction of test genotypes. Thus, GLS rankings of inbred lines based on disease ratings at these plant developmental stages should be useful in prebreeding nurseries and preliminary evaluation trials involving large germplasm populations.

Climate change and the occurrence of downy mildew in Brazilian grapevines

The objective of this work was to evaluate the potential impact of climate change on the occurrence of grapevine downy mildew in Brazil. Seedlings containing four to six leaves were sprayed with a sporangia suspension containing 105 sporangia per milliliter. After spraying, the seedlings were subjected to temperatures of 26, 28, 29.1, 30.4, and 31.8°C for 24 hours. The percentage of diseased leaf area and the latent period were evaluated. Maps of the geographic and temporal distribution of the disease were made considering the monthly average of the mean air temperature and leaf wetness duration for the reference climate or climate normal (1961-1990) and the future climates (2011-2040, 2041-2070, and 2071-2100), considering the A2 and B1 gas emission scenarios, designed by the Intergovernamental Panel on Climate Change (IPCC). Favorability ranges were set and used in logic functions of the geografical information system (GIS) to generate monthly maps for grapevine downy mildew. Rising temperatures interfered with the grapevine downy mildew infections, reduced the disease severity, and increased the latent period. Future climate scenarios indicate a reduction of favorability of downy mildew in Brazil, with variability in the different grape producing regions.

Micronutrient and fungicides management practices to control the Alternaria blight of mustard

Experiments were conducted to evaluate the efficacy of different micronutrients and fungicides against Alternaria brassicae and Alternaria blight on growth and yield contributing attributes of mustard. Among the treatments, T6 showed the highest performance against Alternaria blight in terms of disease incidence. The lowest leaf infection (9.9%), leaf area diseases (2.5%), pod infection (9.3%) and number of spots per pod (0.6) were recorded in T6. Highest leaf infection (56.1%), diseased leaf area (18.31%), pod infection (42.7%) and number of spots per pod (1.9) were recorded in control. The highest yield (1086.0 kg/ha), germination percentage (99.1) and the lowest seed infection (6.5%) of harvested seeds were obtained from the T6, whereas lowest from T1. The performances of micronutrients were better than control but the performances of micronutrients did not differ significantly when it was used in combination with fungicides. DOI: http://dx.doi.org/10.3329/jbas.v38i1.20212 Journal of Bangladesh Academy of Sciences, Vol. 38, No. 1, 61-69, 2014

Differential Susceptibility of Nine Cucurbit Species to the Foliar Blight and Crown Canker Phases of Gummy Stem Blight

Eighteen cucurbit cultivars representing five genera, nine species, and 17 horticultural types were inoculated with Didymella bryoniae in field plots in Charleston, SC, in autumn 2008, autumn 2009, and spring 2011 to determine susceptibility to gummy stem blight. In each year, gummy stem blight cankers occurred more frequently on crowns or main stems of ‘Athena’ muskmelon (Cucumis melo) and ‘Green Striped Cushaw’ squash (Cucurbita argyrosperma) than on all other cultivars except ‘Rocio’ honeydew (Cucumis melo) in 2009, and bottle gourd (Lagenaria siceraria) and Ojakkyo citron (Citrullus lanatus var. citroides) in 2011. Cucurbita moschata was highly resistant to stem cankers. Severity of gummy stem blight on foliage was moderate to severe in autumn 2009, mild to severe in autumn 2008, and very mild in spring 2011 (due to unusually dry weather). Watermelon (Citrullus lanatus var. lanatus) and melon were the most susceptible to foliar blight in 2008 and 2009. In all 3 years, ‘Cheese’ and ‘Bugle’ squash (both Cucurbita moschata), and ‘Judgment III’ and ‘Lioness’ summer squash (C. pepo) were among the cultivars with the least diseased leaf area. C. moschata, C. pepo, C. maxima, and Luffa cylindrica (smooth loofah) were significantly less susceptible to foliar blight than Cucumis melo and three Citrullus lanatus cultivars in 2008 and 2009. This study also is the first documentation of susceptibility of Cucurbita argyrosperma to gummy stem blight.

Evaluation efficiency of severity of angular leaf spot in common bean based on diseased and healthy leaf area

This study compared severity of angular leaf spot in common bean lines, based on the healthy and diseased leaf area, and the graded scale. We used 12 common bean lines in the dry and rainy seasons. Two contiguous experiments were conducted in each season, with and without chemical control of the pathogen. We evaluated the percentage of the healthy and diseased leaf area; severity based on a graded scale and the area under the disease progress curve; and yield. The diseased or healthy leaf area is efficient to evaluate the severity of angular leaf spot with a sample of 20 to 30 leaflets per plot. For all traits, the results of central and border areas did not differ, indicating that the evaluation of border rows is unnecessary and, finally, the severity assessment of the upper plant half can discriminate the lines more efficiently.

Mapping of QTLs involved in resistence to rice blast (Magnaporthe grisea) using Oryza minuta introgression lines

&nbsp; Introgression lines derived from Oryza minuta and O. sativa subsp. japonica var. Junambyeo were crossed for a mapping of the population composed of 112 recombinant lines to identify putative QTLs against rice blast disease using the percentage of diseased leaf area. By using 148&nbsp;Sequence Tagged Site (STS) and Single Sequence Repeat (SSR) markers, five QTLs on chromosomes 6, 7, 9 and 11 and seven epistatic QTLs were identified against two blast isolates (KI307 and KI209). Of them two QTLs (qKI307-2 and qKI209-3) shared a similar position on chromosome 11. O. minuta introgression contributed the resistance allele for all of these QTLs. Combined phenotypic variations by QTL and (E-QTL) accounted for 56.9% against KI307, and 53.4% against KI209. Each QTL could account for the resistance variation between 11 and 24.6%. The resistance from wild introgressions was attributable to a combination of QTLs and epistatic effects between different loci, capable of inducing hypersensitive reactions. Our findings are in support of the strategy of pyramiding major QTLs to develop improved rice varieties with durable broad spectrum resistance against the blast fungus.

Characterization of tomato accessions for resistance to early blight

The purpose of this study was to characterize 50 tomato genotypes of the Vegetable Genebank of the Federal University of Viçosa. They were evaluated together with the controls Débora, Fanny and Santa Clara, in a randomized block design with two replications. The experiment was conducted in a research field of the UFV, from February to May 2007. We evaluated the disease severity, which is the percentage of diseased leaf area. The severity values were transformed into area under the disease progress curve (AUDPC), improving the result visualization. The analysis of variance and grouping of AUDPC means by the Scott-Knott test at 5 % significance were performed. The accessions BGH-2081, BGH-2034, BGH-700, BGH-2057, BGH-2035, BGH-2054, BGH-2018, BGH-2065, BGH-2008, and BGH-2032 had a lower mean AUDPC than the controls and are therefore indicated for future breeding programs.

The Pi40 Gene for Durable Resistance to Rice Blast and Molecular Analysis of Pi40-Advanced Backcross Breeding Lines

Rice blast severely reduces production in both irrigated and water-stressed upland ecosystems of tropical and temperate countries. Nearly 50 blast resistance genes have been identified and some of those are incorporated into several rice cultivars. However, most of the resistance genes break down in a few years because of their race specificity and the rapid change in pathogenicity of the blast fungus (Magnaporthe grisea). The objective of this study was to analyze advanced backcross breeding lines (ABL) possessing the gene Pi40 for durable rice blast resistance. In all, 4 resistant genotypes, 4 japonica cultivars, and 10 monogenic differential rice genotypes with some known resistance genes were bioassayed in the greenhouse using seven sequential plantings and 29 virulent M. grisea isolates of Korea. The genotypes with the Pi40 gene had <3% diseased leaf area, which was significantly below the disease threshold level of 40% considered for durable blast resistance. Moreover, the genotypes with the Pi40 gene expressed compatibility with only two to three virulent M. grisea isolates supporting durability of resistance, in contrast to susceptible cultivars with >50% diseased leaf area and 10 compatible isolates. Of the 10 known resistance genes tested, Piz-t, Piz-5, and Pi9 showed differential reactions to the pathogen isolates in seven plantings. Genotyping of the ABL with 260 simple sequence repeat (SSR) markers revealed rapid conversion toward recurrent parent genotypes with fewer donor chromosomal segments (5.3 to 14.5%). Our study based on a sequential testing and background selection of breeding lines with the resistance gene Pi40 provided valuable information for durable blast resistance breeding in rice.

Screening for Resistance to Leaf Spot Diseases of Spinach

The entire U.S. Department of Agriculture (USDA) spinach (Spinacia oleracea L.) germplasm collection (338 accessions) and 22 commercial cultivars were evaluated for resistance to leaf spot caused by Stemphylium botryosum in a greenhouse trial with two replications in 2004. The resistant and susceptible accessions identified as well as the 22 commercial cultivars were included in a second test in 2005 with four replications to confirm the results. No genotype was completely resistant (immune) to the disease. However, there were significant differences in disease incidence (percent of plants with leaf spot) and severity (percent diseased leaf area) among the genotypes tested. Two accessions from Turkey, PI 169685 and PI 173809, consistently had low disease incidence and severity ratings. Two Spinacia tetrandra and four Spinacia turkestanica accessions screened in these public germplasm tests were all susceptible. None of the commercial cultivars tested consistently had low disease incidence or severity. There was no significant correlation between disease incidence/severity and leaf type (smooth, semisavoy, or savoy). In addition to the public germplasm evaluated, 138 proprietary spinach genotypes (breeding lines and cultivars) were obtained from seed companies and screened along with 10 accessions from the USDA germplasm collection for resistance to Stemphylium leaf spot and Cladosporium leaf spot (caused by Cladosporium variabile) in a greenhouse in both 2004 and 2005. Significant differences in severity of leaf spot were observed among the genotypes for both diseases. For each disease, there was a significant positive correlation in severity ratings of the genotypes between the 2004 and 2005 trials. Information on the relative resistance (or susceptibility) of the spinach germplasm evaluated in this study should be useful for plant breeders to develop leaf spot-resistant cultivars.