Abstract: The Phytophthora complex associated with Castanea sativa Mill. was investigated in five European countries in 35 regions and with respect to various domestication levels. Annual precipitation and length of drought season were the main parameters that regulated the presence of Phytophthora species in the chestnut stands. Seven species of Phytophthora were detected; three of these, P. megasperma, P. cryptogea and P. syringae had not been previously reported on sweet chestnut. P. cinnamomi. P. cambivora and P. citricola were most frequently isolated. P. cinnamomi and P. cambivora were the species significantly associated with declining trees with symptoms of Ink Disease. P. cinnamomi required distinct ecological conditions compared to the other species. P. cinnamomi was never detected in sites characterized by minimum temperatures below 1.4 °C, maximum temperature above 28 °C, or soil pH below 5.4. The results obtained provide useful information for modeling the probability of Ink Disease, crown decline and associated Phytophthora species in chestnut groves in global climatic change scenarios.
Abstract: An experiment was undertaken to study the soil inoculum build up and distribution pattern of Phytophthora in cardamom soils in Kerala, India. Two different locations representing high and low disease intensity were selected. The inoculum distribution was studied at three different depths and distance from the plant base. In high disease pressure area, the Phytophthora propagules are present throughout the season at almost all depths and distance studied whereas in low disease pressure area the population level was comparatively low during April-June months at all the depths and distance. The inoculum build up starts during July and the level became comparatively high during December months at 0-5 cm distance from the plant base. In the high disease pressure area also inoculum build up was noticed during November-December months. The inoculum distribution was noticed at all the depths irrespective of distance from the plant base. It is observed that the inoculum build up occurs only when there is sufficient moisture in the soil as evidenced from the inoculum level in the low disease pressure area. The pH of the soil was found between 5 and 6 which is a congenial condition for the growth of Phytophthora.
Abstract: Aim of this study was to develop sensitive PCR assay for mycotoxin producing Fusarium species. Strains Fusarium oxysporum 4199 and Fusarium culmorum 4044 were used as representatives of this group. Primers JB chosen to demonstrate the affiliation to genus Fusarium were derived from ITS region of rDNA. Gene from trichothecene pathway Tri4 was employed to design primers for toxin biosynthesis. Specificity of PCR based on JB primers was tested on DNA isolated from F. culmorum 4044, F. oxysporum 4199, Aspergillus oryzae 4002 and Mucor circinelloides 4018, Trichoderma sp. Both Fusarium species gave positive reaction, while the later ones did not react. Primers based on Tri4 highly specific sequences were giving positive reaction only with DNA from F. culmorum 4044 and F. oxysporum 4199. DNA isolated from six samples of contaminated wheat grains gave positive result on the presence of genus Fusarium and mycotoxines by optimised PCR protocol using JB and Tri4 primers. The results corresponded to LC/MS analysis that was established quantitatively in all samples to ascertain the amount and type of fusarious mycotoxines.
Abstract: The invasive plant pathogen Phytophthora cinnamomi (Stramenopila, Oomycota) has been introduced into 15 of the 25 global biodiversity hotspots, threatening susceptible rare flora and degrading plant communities with severe consequences for fauna. We developed protocols to contain or eradicate P. cinnamomi from spot infestations in threatened ecosystems based on two assumptions: in the absence of living hosts, P. cinnamomi is a weakly competitive saprotroph; and in the ecosystems we treated, the transmission of the pathogen occurs mainly by root-to-root contact. At two P. cinnamomi-infested sites differing in climate and vegetation types, we applied increasingly robust treatments including vegetation (host) destruction, fungicides, fumigation and physical root barriers. P. cinnamomi was not recovered at three assessments of treated plots 6–9 months after treatments. Given the high rates of recovery of P. cinnamomi from untreated infested soil and the sampling frequency, the probability of failing to detect P. cinnamomi in treated soil was <0.0003. The methods described have application in containing large infestations, eradicating small infestations and protecting remnant populations of threatened species.
Abstract: Vascular wilts are the most important yield limiting diseases of vegetables and caused by both fungal and bacterial pathogens.The major wilt causing fungal pathogenic genera are Fusarium and Verliciflium; while Rafstonia solanacearum is the bacterial
wilt pathogen . These pathogens are a challenge to control because they often survive in soil for long periods and affect the crops throughout the year from across the plant families. The disease symptoms caused by each pathogenic genus are often creating confusions. For the effective plant disease management a thorough knowledge on symptoms caused by various pathogenic organisms, their detection and diagnostics techniques, mode of survival and infection, host range, and favorable conditions is needed. Similarl y, to minimize the crop yield losses due to vascular wilt diseases, approaches like use of resistant varieties/cultivars, selection of suitable chemical fungicides/antibiotics, adopting different cultural practices and application of appropriate biocontrol agents, are to be included in the disease management practices. This review aims to proVide comprehensive information about the vascular wilt diseases of vegetable crops, pathogen detection and disease management.
Abstract: Severe defoliation of green leaves of nutmeg (Myristica fragrans) was observed in major nutmeg growing areas of Thrissur, Emakulam, Idukki and Kottayam districts of Kerala, India, during the southwest monsoon period of 2011. Infection was observed on leaves, shoots and fruits. Symptoms first appeared as dark brown water-soaked lesions on the midrib of the leaves which enlarged and spread along the lateral veins to leaf lamina resulting in blighting. Petioles of the infected leaves showed black discoloration. On young shoots, black lesions were observed which enlarged in size resulting in rotting and drying up of shoots from the tip downwards. Leaf and stem infections resulted in extensive defoliation. The causal organism was identified as Phytophthora ramorum based on cultural, pathogenicity and morphological analyses. This is thought to be the first report of P. ramorum causing leaf fall and shoot rot of nutmeg.
Abstract