Abstract: Most selections of black pepper are susceptible to the Phytophthora foot rot caused by Phytophthora capsici. Studies were undertaken to quantify the amount of secondary metabolites - piperine and oleoresins - in the vegetative plant parts of the susceptible selection KS27, tolerant selection P24 (both P. nigrum) and the resistant Piper species, P. colubrinum; and to study if they had any effect on the vegetative growth of the pathogen in vitro. The P. nigrum selections, KS27 and P24, especially the latter, had higher concentrations of piperine in the roots than the leaves or stems. Synthetic piperine was found to inhibit the vegetative growth of P. capsici in vitro, at concentrations of 0.4% and above. The oleoresin concentration was highest in the leaves, followed by the roots and least in the stems; the trend was the same in all three Piper plants with P. colubrinum recording the highest values. A significant inhibition in the growth of P. capsici was recorded when oleoresin from roots was incorporated in the media, less so in that containing leaf oleoresin, and an increase in growth in the presence of stem oleoresins. As the trend was the same in all three plants, no correlation could be drawn between inhibition of growth and susceptibility/tolerance/resistance to P. capsici.
Abstract:Phytophthora term blight caused by Phytophthora capsici is a serious threat to vegetable production worldwide. Currently, no single method provides adequate control of P. capsici. Greenhouse studies were conducted to evaluate the potential of the use of bacilli plant growth-promoting rhizobacteria (PGPR) for control of Phytophthora blight on squash. PGPR strains were applied as a soil drench 1 and 2 weeks after planting (WAP), and P. capsici was applied to squash roots at 3 WAP. PGPR strains SE34 and SE49 applied at 1 × 108 CFU/ml significantly (P < 0.05) reduced disease severity in all three repeated greenhouse trials compared to the nontreated control. Treatments with PGPR strains SE52, SE76, INR7, IN937a, and IN937b demonstrated significantly lower disease in two of three trials when compared with the nontreated control. Certain PGPR strains applied as 2-, 3-, and 4- strain mixtures significantly reduced disease severity. Treatment with T4 + SE56 demonstrated significantly lower levels of disease than any individual PGPR strain, indicating either an additive or synergistic effect on disease reduction achieved by mixing PGPR strains. Others such as INR7 + T4 + SE56 and INR7 + IN937a + T4 + SE56 have a high potential to significantly improve the control efficacy. When applied as seed treatments, only PGPR strain1PC-11 at 1 × 105 CFU/seed resulted in significant reduction in Phytophthora blight disease in all trials, while PGPR strains SE56 at 1 × 105 and 1 × 106 CFU/seed, GB03 at 1 × 105 CFU/seed, 1PC-11 at 1 × 106 CFU/seed, and 1PN-19 at 1 × 104 CFU/seed significantly suppressed the disease in two of three trials. These results indicate that certain PGPR strains are effective against P. capsici on squash, and improved disease control can be achieved by multiplexing them.
Abstract: Phytophthora root and crown rot is a plant disease responsible for important economic losses in protected pepper crops. A greenhouse experiment was carried out in a temperate climate region (northern Spain) to assess the effects of repeated biodisinfection after three consecutive crop seasons with different organic amendments (a non-composted mixture of sheep manure and chicken litter, a semicomposted mixture of horse manure and chicken litter, Brassica carinata dehydrated pellets plus Sinapis alba fresh green manure) on disease incidence, crop yield and soil quality. Biodisinfection treatments were found to improve soil water properties through reduction in soil bulk density and increased water infiltration. Biodisinfested soils showed higher values of physicochemical and microbial properties than control (untreated) and plastic-mulched soils. In plots treated with the non-composted or semicomposted mixture, the observed higher levels of microbial activity were strongly related with an increase in soil microbial biomass. Brassica-Sinapis treatment had a weaker effect on soil properties than animal manure-based treatments. However, highest counts of total bacteria, actinomycetes and Pseudomonas spp. were found in Brassica-Sinapis-treated soils. It was concluded that repeated biodisinfection for the control of Phytophthora root and crown rot in protected pepper crops located in temperate climate regions can improve soil quality and suppressiveness, as well as allow for a reduction in the dose of organic amendment needed for biodisinfection. Among the studied organic amendments, the semicomposted amendment was the best option in terms of reduction in disease incidence.
Abstract: We developed an Agrobacterium tumefaciens-mediated transformation system for Eucalyptus urophylla using hypocotyl explants. Antibiotic concentrations, pre-culture times, pH of the inoculation medium and co-culture times were optimised. Pre-cultured hypocotyl explants were co-cultured with A. tumefaciens strain EHA105 harbouring the binary vector pPBR-2 containing the Rs-AFP2 gene, which encodes an antifungal protein, under the control of the prp1-1 promoter, for six days and were then transferred to selective callogenesis-inducing medium containing kanamycin and cefotaxime. Calluses developed shoots and were cultured in an elongation medium and finally multiplied. The integration of T-DNA into the genome of transgenic E. urophylla was confirmed by polymerase chain reaction (PCR). The reverse transcription (RT)-PCR results showed that Rs-AFP2 gene expression could be detected only after the transformed plants were inoculated with Phytophthora capsici 60 hours after inoculation. These results indicated that the prp1-1 promoter was inducible and Rs-AFP2 could enhance the resistance of E. urophylla to P. capsici. This protocol enabled effective transformation and regeneration of E. urophylla.
Abstract: Greenhouse studies were performed to determine the reactions of 10 "California Wonder" (Capsicum annuum) accessions to the three forms of Phytophthora blight (root rot, stem blight and foliar blight) caused by Phytophthora capsici. Differences in root rot, stem blight and foliar blight severities among accessions were significant. The accessions consistently differentiated into two groups across the three disease syndromes. Simple sequence repeat (SSR) markers showed variability both within and between accessions of California Wonder. The variability in the responses to the three forms of Phytophthora blight does not warrant its usefulness as a standard susceptible control in studies involving the Capsicum-P. capsici patho-system.
Abstract: Field survey was undertaken in major tomato growing districts of the Karnataka and other states in Southern Part of India to isolate bacterial wilt pathogen Ralstonia solanacearum from wilted tomato plants and soil samples. A total of 100 isolates named as RS1-RS100 were subjected to cultural, morphological, biochemical and pathogenicity studies. Significant variations existed among the isolates with respect to rate, type of growth and colony colour. According to the pathogenicity tests conducted, around 57% of the isolates were found to be highly virulent. The population build up of the pathogen on the root system was found to have played an important role in relation to the pattern of occurrence of pathological wilting among tomato plants in the field. Bacteria with the same characteristics as those inoculated were re isolated from the infected plants, uninoculated plants remained healthy.
Abstract: The aim of this study was to evaluate the efficacy of selected bacterial strains against the wheat soil-borne pathogen Fusarium graminearum under greenhouse conditions. The most potent isolates were 3 isolates out of 18 isolates, which have numbers 3, 9 and 10 with in vitro inhibition index 42.5%, 41.3% and 46.3% respectively. Isolates 3 and 10 were selected for the following experiments. Isolates 3 and 10 were identified as Bacillus subtilis MAA03 and Pseudomonas fluorescens MAA10, respectively according to International Identification Keys and, confirmed by using Biolog system and 16S rDNA where the strains exhibited more than 99.5% sequence identity. Their close taxonomic relationship was further documented by phenotypic similarities. The using of B. subtilis and P. fluorescens separately or in mixture as biocontrol agent against F. graminearum on wheat significantly increased the final germination percent, the mean daily germination and germination index of wheat cultivar, while the mean germination time was significantly decreased relative to infested control. The final infection percent, the mean daily infection and infection index were decreased significantly, while the mean infection time was significantly increased relative to infested control. The use of P. fluorescens as biocontrol agent was the most efficient than B. subtilis or in mixture and the best treatment was seed coating. The application of B. subtilis and P. fluorescens separately or in combination significantly affected the growth parameters of wheat cultivar Tabuki, the root length was significantly increased in seed coating and seed soaking treatments, while non-significantly decreased in case of soil drench treatment relative to infested control. Shoot length was significantly decreased in case of seed coating treatment relative to infested control. The shoot fresh and dry weights were significantly increased in seed coating and seed soaking treatments relative to infested control. The root fresh and dry weights were significantly increased in seed coating and seed soaking treatments relative to infested control. The number of leaves was significantly increased in all treatments relative to infested control.
Abstract: The Fusarium wilt of tomato (Lycopersicon esculentum Mill.) caused by F. oxysporum f.sp. lycopersici (Sacc.) Snyder and Hansen is recognised as one of the most devastating disease in major tomato growing regions worldwide. For eco-friendly and sustainable management of the disease, 88 Trichoderma isolates belonging to 8 species of the genus, T. viride, T. virens, T. harzianum, T. hamatum, T. piluliferum, T. koningii, T. pseudokoningii and T. longibrachiatum were evaluated against the pathogen in dual culture and through production of volatile and non-volatile metabolites. T. viride isolate (TV19) followed by T. harzianum isolate (TH7) and T. virens isolate (TVr5) showed maximum inhibition to mycelial growth of the pathogen. The potential isolates were evaluated as seed, soil and combined seed and soil treatments in pot experiment. All the treatments resulted in significant reduction in mortality of tomato seedlings and improvement in the plant growth parameters. The highest seed germination percentage (81.11%) and control of seedling mortality (61.63%) were obtained in combined seed and soil treatment with T. viride (TV19). The isolates were evaluated under field conditions during 2010 and 2011 cropping season in randomized block design in three replications. The results showed that combined seed and soil treatment with TV19 recorded the least wilt incidence (9.30%) as compared to the control (43.49%). This treatment produced higher yield (292.61 qha-1) than control (102.64 qha-1).
Abstract: The effectiveness of bacteria of the genera Sphingomonas and Bacillus, and yeasts of the genera Cryptococcus, Rhodotorula, and Saccharomyces as biological control agents against pathogens colonizing winter wheat, was tested in laboratory conditions. All of the tested yeast isolates had an inhibitory effect on the development of F. sporotrichioides colonies. Under the same conditions, the Sphingomonas S 11 isolate was antagonistic against F. avenaceum, F. culmorum, F. tricinctum, and F. graminearum. The seedlings of winter wheat cv. Sumai treated with a suspension of Sphingomonas S 11 bacteria and inoculated with F. culmorum demonstrated significantly fewer infection symptoms than unprotected seedlings that were inoculated with the above-mentioned pathogen.
Abstract: Two biological control practices are the use of suppressive growing media and the application of biological control agents (BCAs). The goals of this study were: (i) to screen 584 potential BCAs obtained from Fusarium wilt (FW) suppressive growing media; (ii) to evaluate in greenhouse conditions selected BCAs in three growing media with different degrees of suppressiveness of tomato FW. Two isolates selected after screening were identified as Fusarium solani (305) and Streptomyces sp. (A19). Results showed that tomato FW was reduced and total production was improved when both BCAs were applied to a conducive medium (coir fiber). In highly suppressive growing medium (grape marc compost), A19 and 305 inoculations did not improve suppressiveness. In moderately suppressive growing medium (cork compost), only A19 improved this compost to natural grape marc compost suppressiveness level. Therefore, compost suppressiveness of tomato FW depended on the nature of the compost and on the isolates applied.
Abstract