Genetic diversity, aggressiveness and metalaxyl sensitivity of Pythium aphanidermatum populations infecting cucumber in Oman

Seventy three isolates of Pythium aphanidermatum obtained from cucumber from four different regions of Oman and 16 isolates of muskmelon from the Batinah region in Oman were characterized for aggressiveness, sensitivity to metalaxyl and genetic diversity using AFLP fingerprinting. Twenty isolates of P. aphanidermatum from diverse hosts from different countries were also included in the study. Most isolates from Oman were found to be aggressive on cucumber seedlings and all were highly sensitive to metalaxyl (EC50 0.05), which implies a lack of host specialization in P. aphanidermatum on these two hosts in Oman. AFLP analysis of all isolates using four primer-pair combinations resolved 152 bands, of which 61 (~40%) were polymorphic. Isolates of P. aphanidermatum from Oman and other countries exhibited high genetic similarity (mean = 94.1%) and produced 59 different AFLP profiles. Analysis of molecular variance indicated that most AFLP variation among populations of P. aphanidermatum in Oman was associated with geographical regions (FST = 0.118; P < 0.0001), not hosts (FST = -0.004; P = 0.4323). These data were supported by the high rate of recovery (24%) of identical phenotypes between cucumber and muskmelon fields in the same region as compared to the low recovery (10%) across regions in Oman, which suggests more frequent movement of Pythium inoculum among muskmelon and cucumber fields in the same region compared to movement across geographically separated regions. However, recovering clones among regions and different countries may imply circulation of Pythium inoculum via common sources in Oman and also intercontinental spread of isolates

Potential of Omani Flora as Source of Natural Products for Control of Pulse Beetle, Callosobruchus chinensis

Extracts of eight plants from the Omani flora were tested for their effects on oviposition, adult emergence from eggs and mortality of the pulse beetle, Callosobruchus chinensis. Observations were made on the number of eggs laid on kidney bean seeds treated with extracts, adult emergence from seeds and mortality of adults exposed to treated seeds. The number of eggs laid and the adults emerged from seeds treated with extracts prepared from ethanol were significantly less than from seeds treated with extracts prepared from methanol. The mortality of beetles released on grains treated with A. squamosa was l00% within 2 and 6 days in ethanol- and methanol-based extracts, respectively

Screening Potato Varieties for Cultivation in Arid Regions: Effect of Planting Date on Emergence of Imported and Locally-Produced Seeds

Potato is new as a major crop in arid regions. Due to its food value, expanding production and increasing consumer demand, it is being considered as a strategic crop. Production is based on yearly import of seed potatoes from Europe. Productivity of potato could be increased by targeted selection of varieties for local adaptation, by choosing the adequate conditions for planting and through proper seed management. The seed and its imposed planting time were found to be incompatible with optimum stand development for the crop, resulting in a loss of potential yield. The young physiological age and persisting dormancy of seed prevented early emergence of sprouts from a mid-November planting time. When planted on 11 consecutive dates, varieties showed a significant improvement of emergence rates with delayed planting time. Emergence rate doubled as planting was delayed from mid November to mid December. Emergence rate results for imported tubers were confirmed over three consecutive growing seasons and contrast with emergence data for locally produced seed planted at the same or earlier dates

Insecticidal and Repellent Properties of Subtropical Plant Extracts Against Pulse Beetle, Callosobruchus chinensis

Extracts of eight plants local to Oman, namely Qarat (Acacia nilotica), Mustafal (Annona squamosa), Shereesh (Azadirachta indica), Luban (Boswellia sacra), Kheshkhash (Crotolaria juncea), Zebrot (Jatropha dhofarica) Yas, (Myrtus communis) and Suwwad (Suaeda aegyptiaca) were prepared by steeping shaded dried leaf/ seed powder of each plant in water and solvent (methanol or ethanol). The extracts were tested for their insecticidal and repellent properties against the pulse beetles, Callosobruchus chinensis. The extracts from the seeds of A. squamosa recorded l00% mortality of beetles within twenty and four hours of their exposure to methanol and ethanol extracts, respectively. The other extracts that caused high mortality were from A. nilotica, C. juncea, M. communis and S. aegzptiaca in methanol and B. sacra, J. dhofarica, S. aegptiaca and commercial neem in ethanol. Extracts of M. communis in methanol were highly repellent to the beetles compared to other extracts. Legume seeds treated with extracts of A. squamosa were not repellent, rather the beetles were attracted to them

Clonal structure of Ceratocystis manginecans populations from mango wilt disease in Oman and Pakistan

Ceratocystis manginecans has recently been described from Oman and Pakistan where the fungus causes a serious wilt disease of mango. In both countries, the disease has moved rapidly throughout mango producing areas leading to the mortality of thousands of mango trees. The disease is associated with the infestation of the wood-boring beetle Hypocryphalus mangiferae that consistently carries C. manginecans. The aim of this study was to consider the population structure of C. manginecans isolated from Oman and Pakistan using microsatellite markers and amplified fragment length polymorphisms (AFLPs).Population genetic analysis of C. manginecans isolates from diseased mango tissue and bark beetles associated with the disease in Oman and Pakistan, showed no genetic diversity. The apparently clonal nature of the population suggests strongly that C. manginecans was introduced into these countries as a single event or from another clonal source.Tree Protection Co-operative Programme (TPCP), National Research Foundation (NRF), South Africa and the Ministry of Agriculture and Fisheries in Sultanate of Oman.http://link.springer.com/journal/13313hb201

Mango sudden decline pathogen, Ceratocystis manginecans, is vectored by Hypocryphalus mangiferae (Coleoptera : Scolytinae) in Oman

In Oman, the bark beetle Hypocryphalus mangiferae is closely associated with trees affected by mango sudden decline disease caused by Ceratocystis manginecans. Although it has previously been assumed that this beetle plays a role in the dispersal of the pathogen, this has not been established experimentally. The aim of this study was to determine whether H. mangiferae vectors C. manginecans from infected to healthy mango trees. A survey conducted in northern Al Batinah region of Oman revealed that H. mangiferae was closely associated with mango sudden decline disease symptoms and it was found on trees in the early stages of the disease. Healthy, 2- year-old mango seedlings were exposed to H. mangiferae collected from diseased mango trees. Seedlings were infested by the bark beetles and after 6 weeks, typical mango sudden decline disease symptoms were observed. Ceratocystis manginecans was isolated from the wilted mango seedlings while uncolonized control seedlings remained healthy. The results show that H. mangiferae vectors C. manginecans in Oman and is, therefore, an important factor in the epidemiology of this disease.The National Research Foundation (NRF)http://www.springerlink.com /content/100265

Evaluation of mango cultivars for resistance to infection by ceratocystis manginecans

Ceratocystis manginecans has been reported to cause a serious wilt disease of mango in Oman and Pakistan. To identify plants resistant to this disease, 30 mango cultivars were artificially inoculated with isolates of C. manginecans in three trials. Statistical analysis revealed significant differences (P < 0.0001) in lesion lengths among mango cultivars. Similarly, there were significant differences in the aggressiveness of the isolates used for inoculations. However, in trials where more than one isolate was used, there was no significant isolate x cultivar interaction suggesting that isolates do not affect the ranking of cultivars as susceptible or resistant. Cultivar ‘Pairi’ and local mango cultivars had the longest lesions and were ranked as highly susceptible. In contrast, cultivars ‘Hindi Besennara’, ‘Sherokerzam’, ‘Mulgoa’, ‘Baneshan’, ‘Rose’ and ‘Alumpur Baneshan’, had the smallest lesions and are considered as relatively resistant against C. manginecans. The inoculation results are concurrent with the incidence of wilt of these cultivars under field conditions.The Tree Protection Co-operative Programme (TPCP), National Research Foundation (NRF) in South Africa, the Ministry of Agriculture and Sultan Qaboos University in Sultanate of Oman and Food and Agriculture organization (FAO).http://www.actahort.org/am201

Ceratocystis manginecans associated with a serious wilt disease of two native legume trees in Oman and Pakistan

A serious wilt disease has recently been found on Prosopis cineraria (Ghaf) in Oman and on Dalbergia sissoo (Shisham) in Pakistan. Disease symptoms on both these native, leguminous hosts include vascular discolouration and partial or complete wilt of affected trees. A species of Ceratocystis was consistently isolated from symptomatic material. Morphological comparisons and analyses of DNA sequence data of the ITS, β-tubulin, and EF 1-α gene regions showed that the Ceratocystis isolates obtained from both tree species represent C. manginecans. This is the same pathogen that is causing the devastating mango sudden decline disease in Oman and Pakistan. This is also the same pathogen that has been reported causing a wilting disease on Acacia mangium in Indonesia. Cross inoculation with C. manginecans isolates from P. cineraria, D. sissoo and mango showed that the fungus can cause disease on all three trees.Tree Protection Cooperative Programme (TPCP), University of Pretoria, South Africa, and the Ministry of Agriculture and Fisheries, Omanhttp://link.springer.com/journal/13313hb201

Factors Affecting the Levels of Eyespot and Fusarium Foot-Rot on Winter Wheat cv. Hereward in Cereal Monocrops and Wheat Clover Bicrops

Various factors influencing the amount of disease on the stem-base of wheat, when grown as a component of a bicrop, with white clover, are described. The amount of crop debris on the soil surface remained higher in monocrop than bicropped plots. Furthermore, the rate of debris decay was faster in bicrops than in monocrops. Population levels of P. herpotrichoides and Fusarium spp. were higher on debris within bicrops than on debris within monocrop plots. However, because debris decomposition was more rapid in bierops, inoculum availability was of shorter duration in bicrops than monocrop plots. ln soil, populations of P. herpotrichmoides were greater in bicropped plots than in monocrops, although no significant differences were observed for Fusarium spp. population levels. Pathogen cross-infection between bicrop components and changes in microclimate within crop canopies were shown to occur, and isolates of Fusarium from clover were shown to induce significant levels of disease on cereal seedlings. The effects of each of these factors on disease development are discussed in relation to previous reports of disease levels in the field

Factors Affecting the Levels of Eyespot and Fusarium Foot-Rot on Winter Wheat cv. Hereward in Cereal Monocrops and Wheat Clover Bicrops

Various factors influencing the amount of disease on the stem-base of wheat, when grown as a component of a bicrop, with white clover, are described. The amount of crop debris on the soil surface remained higher in monocrop than bicropped plots. Furthermore, the rate of debris decay was faster in bicrops than in monocrops. Population levels of P. herpotrichoides and Fusarium spp. were higher on debris within bicrops than on debris within monocrop plots. However, because debris decomposition was more rapid in bierops, inoculum availability was of shorter duration in bicrops than monocrop plots. ln soil, populations of P. herpotrichmoides were greater in bicropped plots than in monocrops, although no significant differences were observed for Fusarium spp. population levels. Pathogen cross-infection between bicrop components and changes in microclimate within crop canopies were shown to occur, and isolates of Fusarium from clover were shown to induce significant levels of disease on cereal seedlings. The effects of each of these factors on disease development are discussed in relation to previous reports of disease levels in the field