Regulation of monocarpic senescence of Brassica campestris by the developing pods

Senescence of Brassica campestris L. cv. B-9 was studied with regard to seed maturation and source-sink relationships. In normal control plants leaf senescence (as determined by the change in chlorophyll level) started and proceeded in a progressive manner from base to apex during the period of early pod setting. Complete yellowing of the leaves occurred well before the seed maturation and pod wall senescence. The pod wall always senesced before the attainment of final seed weight. In two different sets of acrocarpous plants containing 65 pods and 10 pods, respectively, leaf senescence was delayed during the pod filling period. It started non-sequentially after complete yellowing and senescence of the pod wall. The degree of leaf senescence at the post-pod filling stage was almost proportional to the number of pods present. When peduncles of the acrocarpous 10-podded plants were removed after the pod filling stage of the plant, leaf senescence was delayed compared to plants whose pedicels were removed, although the senescence pattern of the upper three leaves was nonsequential in both cases. Defruiting at an early stage of development delayed leaf senescence, although the pattern of such senescence remained unaltered (i.e. nonsequential). Defoliation hastened the seed-filling process and pod wall senescence. Plants containing fewer pods had higher average seed weight, although yield per plant was reduced.
These results suggest that the pod wall serves as a temporary as well as intermediary storage organ and that foliar senescence is not directly related to seed maturation. The possible cause of uncoupling between foliar senescence and seed development is discussed.     

Effect of cocoa pod age on egg distribution and egg parasitism of the cocoa pod borer in Malaysia

The effects of pod age on oviposition, and on egg and larval survival of the cocoa pod borer (CPB), Conopomorpha cramerella (Snellen), were investigated. CPB were allowed to oviposit on a batch of 50 pods for a period of 7 days over several exposure dates. Numbers of CPB eggs/pod and survival to larval emergence from the pods were recorded. Pods were harvested when ripe and analyzed for larval survival within the pod. The oviposition pattern varied with pod age. Older pods less than 7 weeks before ripening (WBR) were preferred, suggesting greater nutritional value or chemical attraction of the older pods. The proportion of eggs parasitized by Trichogrammtoidea bactrae fumata Nagaraja (TBF), the number of eggs lost and the proportion surviving to larval emergence from the pod were independent of pod age. Egg parasitism was low, implying that TBF was not an effective natural enemy. Mass-releases of TBF should be intensified during cropping periods with higher proportions of susceptible pods (<10 WBR). Survival of larvae in the presclerotic layer (preSCL) was high and independent of pod age. Larval mortality at the SCL (sclerotic layer) was dependent on pod age and was high in older pods. Larval density influenced the survival of larvae inside the pod and was dependent on pod age. Larval mortality associated with SCL hardness and thickness is one of the criteria for the selection of CPB resistant cocoa clones.     

First Report of Choanephora Rot of Okra Caused by Choanephora cucurbitarum in Korea

In July and August 2013, blossom blight and soft rot of pods were observed on okra in experimental fields in Iksan and Jeju, Korea. Infection started in fading flower petals, spread to entire flowers and young pods, resulting in blighted blossoms and soft rot of pods. Severe infection caused early falling of blossoms and fruit drop, reducing plant vigour in the summer season. On the basis of the morphological characteristics and phylogenetic analyses of two molecular markers ITS rDNA and D1/D2 region of the LSU, the fungus was identified as Choanephora cucurbitarum. A pathogenicity test was carried out to fulfil Koch's postulates. To our knowledge, this is the first report of C. cucurbitarum on okra in Korea.     

Influence of the endomycorrhizal fungus Glomus mosseae on the development of peanut pod rot disease in Egypt

Glomus mosseae and the two pod rot pathogens Fusarium solani and Rhizoctonia solani and subsequent effects on growth and yield of peanut (Arachis hypogaea L.) plants were investigated in a greenhouse over a 5-month period. At plant maturity, inoculation with F. solani and/or R. solani significantly reduced shoot and root dry weights, pegs and pod number and seed weight of peanut plants. In contrast, the growth response and biomass of peanut plants inoculated with G. mosseae was significantly higher than that of non-mycorrhizal plants, both in the presence and absence of the pathogens. Plants inoculated with G. mosseae had a lower incidence of root rot, decayed pods, and death than non-mycorrhizal ones. The pathogens either alone or in combination reduced root colonization by the mycorrhizal fungus. Propagule numbers of each pathogen isolated from pod shell, seed, carpophore, lower stem and root were significantly lower in mycorrhizal plants than in the non-mycorrhizal plants. Thus, G. mosseae protected peanut plants from infection by pod rot fungal pathogens. Accepted: 10 February 2000     

A small-scale screening technique for evaluating fungicides against Phytophthora palmivora pod rot of cocoa

Plots of clonal Trinitario cocoa were sprayed with fungicides in the field. Ripe pods were harvested from the trial plots and artificially inoculated with Phytophthora palmivora using various techniques, the most suitable of which proved to be the zoospore spot method. Percentage infection results from the spot inoculation tests agreed well with the field percentage infection results and it was concluded that field spraying followed by zoospore spot inoculation of detached pods is a suitable preliminary screening technique for fungicides. Three systemic fungicides metalaxyl, aluminium tris (ethyl phosphonate) and DPX-3217 in a mixture with captafol and copper oxychloride were compared with the protectant cuprous oxide. Metalaxyl was found to be the most effective of the systemic fungicides and when applied at the rate of 0·44 g ai/ha every 8 wk it gave a similar reduction in percentage infection to 4 weekly applications of cuprous oxide at the rate of 4·4 kg Cu⁺⁺/ha during the wetter part of the year when pod rot is most severe.     

Effects of artificial defoliation on reproductive allocation in the common vetch,Vicia sativa (Fabaceae: Papilionoideae)

Previous field experiments have shown that, for the annual herb Vicia sativa, leaf area lost to herbivory results in reduced number of fruit (pods) produced per plant as well as fewer seeds per pod. We conducted a controlled garden experiment to determine the precise relationship between level of defoliation and various measures of maternal fitness through fruit and seed. We employed manual clipping of individual leaflets of newly produced leaves to 25% increments of damage (from 0% to 100%) over the entire period of development and flowering of these annual herbs, harvesting pods when filled but not dehisced. We found significant reduction in number of pods, number of seeds, total seed mass, and individual seed mass with leaf area lost. Even with the highest levels of defoliation over the life of the individual, plants still produced a substantial number of pods and seeds. Seeds produced by plants in all treatment groups showed similar percentages of germination and time to germination.     

Effect of mycorrhiza and biofertilisers on reducing the incidence of Fusarium root and pod rot diseases of peanut

Pathogenicity tests of twenty-six fungal isolates were tested on peanut plants (Giza 5 cv.) and the results revealed that, Fusarium oxysporum isolate (No. I) followed by F. solani (No. II) then F. moniliforme (No III) significantly caused highest incidence of root rot disease. Also, F. moniliforme (No III) followed by F. solani (No II) then F. oxysporum (No I) gave the highest incidence of pod rot disease. The effectiveness of vescular arbuscular-mycorrhiza (VAM) at different application rates on the incidence of root rot, pod rot diseases and plant growth parameters of peanut was studied. All soil treatments with each rate of VAM significantly reduced root and pod rot diseases compared with control (rate 0%). The best reduction in the severity of both diseases with VAM was found at the rate of 3%. Application of rhizobacterin, microbin and cerialin biofertilisers at the different concentrations decreased the severity of both root rot and pod rot severity diseases compared with non-treated seeds. The greatest reduction in both diseases was achieved at a concentration of 8/100?g seeds. The highest number of pods and fresh weight (g) was achieved in seed supplemented with each biofertiliser at concentration of 8/100?g seed.     

Effect of Fruiting Traits on the Field Resistance of Cocoa (Theobroma cacao L.) Clones to Phytophthora megakarya

The effects of some traits of field resistance (precocity and duration of the fruiting cycle, age of diseased fruit and vertical pod distribution on the tree) to Phytophthora megakarya of four known cocoa clones were studied in an on‐station clonal plot planted in 1982 in the south‐west of Cameroon. Weekly observations of fruit set and development, black pod and rainfall were carried out during three growing seasons (1999, 2000 and 2001). The study confirmed the previous field and laboratory assessments of resistance of these clones based on the mean percentages of rotten pods obtained annually. The present study has permitted the identification of fruit aged 2–3 months as the highly susceptible stage of development in the most susceptible clone. In addition, precocity and pod cycle duration varied significantly among the clones. The earlier the pod cycle began, the more susceptible was the clone: the most resistant clone started flowering 1 month after the most susceptible clone and therefore escaped the peak of disease severity. Rainfall intensity greatly modified the incidence of the disease in 2001, with high yield losses occurring in all four clones (70–93%), but their ranking remained stable over the 3 years. The spatial distribution of pods on the trees showed that pods on the trunk were more likely to become diseased than those on the branches, but its effect as a clone resistance component is variable among the four clones; the resistant clone producing more pods on the trunk and the susceptible clone more in the canopy.     

Role of foliar hemibiotrophic and fruit resistance in anthracnose‐resistant strawberry genotypes for annual hill plasticulture systems

Anthracnose fruit rot (AFR) caused by Colletotrichum acutatum is one of the most devastating diseases of strawberry (Fragaria × ananassa) in plasticulture systems in the Southeast US. Host resistance offers the best option to limit crop losses in both nursery and fruiting fields. To evaluate levels of anthracnose resistance and elucidate the role of foliar and fruit resistance in overall field AFR resistance, we tested 14 strawberry genotypes including numerous selections from the North Carolina State University strawberry breeding programme. Inoculations of plug plants with three representative C. acutatum isolates prior to field‐set indicated that the commercially standard cultivar Chandler was highly susceptible, with an average fruit rot incidence of over 72% the following spring. In contrast, breeding lines such as NC C99‐13 and NC C02‐63 showed superior resistance with AFR incidence values of 23.6% and 11.1%, respectively, and showed superior marketable yields. An average hemibiotrophic infection (HI) severity on foliage (percent leaf area covered with acervular growth after paraquat treatment and incubation) did not correlate (r = 0.57) well with in vitro AFR severity on detached fruit, indicating different mechanisms may be operative for resistance to foliar HI and fruit rot resistance. Multiple regression analysis indicated that in vitro fruit rot resistance expressed by lesion diameter and severity of foliar hemibiotrophic infections may be utilized to predict field AFR incidence. Strawberry genotypes bred for resistance against both fruit rot and foliar HI could be effectively selected by using rank‐sum classification methods and this process offers an effective strategy to advance selections for superior AFR field resistance.     

Transcriptional profile of Pseudomonas syringae pv. phaseolicola NPS3121 in response to tissue extracts from a susceptible Phaseolus vulgaris L. cultivar

Background  

Pseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). This disease affects both foliage and pods, and is a major problem in temperate areas of the world. Although several bacterial genes have been determined as participants in pathogenesis, the overall process still remains poorly understood, mainly because the identity and function of many of the genes are largely unknown. In this work, a genomic library of P. syringae pv. phaseolicola NPS3121 was constructed and PCR amplification of individual fragments was carried out in order to print a DNA microarray. This microarray was used to identify genes that are differentially expressed when bean leaf extracts, pod extracts or apoplastic fluid were added to the growth medium.     

Characterization of leaf senescence and pod development in soybean explants

Excised soybean (Glycine max [L.] Merrill) cv Anoka leaf discs tend to remain green even after the corresponding intact leaves have turned yello on fruiting plants. We have found that explants which include a leaf along with a stem segment (below the node) and one or more pods (maintained on distilled H₂O) show similar but accelerated leaf yellowing and abscission compared with intact plants. In podded explants excised at pre-podfill, the leaves begin to yellow after 16 days, whereas those excised at late podfill begin to yellow after only 6 days. Although stomatal resistances remain low during the first light period after excision, they subsequently increase to levels above those in leaves of intact plants. Explants taken at mid to late podfill with one or more pods per node behave like intact plants in that pod load does not affect the time lag to leaf yellowing. Explant leaf yellowing and abscission are delayed by removal of the pods or seeds or by incubation in complete mineral nutrient solution or in 4.6 micromolar zeatin. Like chorophyll breakdown, protein loss is accelerated in the explants, but minerals or especially zeatin can retard the loss. Pods on explants show rates and patterns of color change (green to yellow to brown) similar to those of pods on intact plants. These changes start earlier in explants on water than in intact plants, but they can be delayed by adding zeatin. Seed dry weight increased in explants, almost as much as in intact plants. Explants appear to be good analogs of the corresponding parts of the intact plant, and they should prove useful for analyzing pod development and mechanisms of foliar senescence. Moreover, our data suggest that the flux of minerals and cytokinin from the roots could influence foliar senescence in soybeans, but increased stomatal resistance does not seem to cause foliar senescence.     

First Detection of Root Rot and Foliar Blight on Pittosporum (Pittosporum tenuifolium) Caused by Pythium irregulare in Italy

During 2013, a new root rot and leaf blight was detected on potted Pittosporum tenuifolium cv. ‘Silver Queen’ plants in a nursery located in the Catania province (eastern Sicily, Italy). On the basis of morphological and cultural features as well as internal transcribed spacer sequence data, the causal agent was identified as Pythium irregulare. Koch's postulates were fulfilled by pathogenicity tests carried out on potted P. tenuifolium cv. ‘Silver Queen’ plants. To our knowledge, this is the first detection of P. irregulare root rot and foliar blight disease on P. tenuifolium in Europe, and it is the first detection using molecular methods for this oomycete pathogen in Italy.     

Growth of broad beans infected by Uromyces viciae-fabae

The effect of artificially regulating the level of a rust infection with Uromyces viciae-fabae (Pers.) Schroet. on the growth and yield of two cultivars of Viciafaba L. (broad beans) was examined in 1973/74. Disease decreased leaf area ratio without increasing net assimilation rate particularly during the stage of ‘pod filling’. Consequently, assimilate supply to developing beans was diminished and the weight of beans per pod and yield of beans per plant decreased. This is unlike the effect of Botrytis fabae Sard, on broad beans which reduces yield by decreasing the number of pods per plant. This suggests that the two leaf spotting pathogens decrease yield in different ways and so may require different approaches to minimise yield losses.     

Crop Growth, Disease and Yield Components of Rusted Phaseolus Beans in Ethiopia

Crop growth and disease epidemics in sprayed and non-sprayed bean plots, artificially infected with rust (Uromyces appendiculatus) 3 weeks after emergence. were assessed weekly in two cultivars, at two locations for two seasons. Disease intensity was regulated by the application of a fungicide at 5 spray frequencies. Fungicide application influenced leaf area index (LAI) and reduced rust intensity. The fungicide had no significant effect on other diseases and dead leaf area. Fungicide application increased seed yield (SY) by increased numbers of pods per plant (PP). Rust severity was strongly correlated with pustule density but the overall relationships among rust assessment parameters depended on cultivar and location. Seed yield and pods per plant were highly correlated with LAI. The relationships between LAI and seeds per pod or seed weight depended on cultivar and location. Overall rust assessment parameters (rust severity and pustule density) showed close, negative relationships with seed yield. seed weight and pods per plant but not with seeds per pod. The relationships obtained in the partially resistant line 6-R-395 were less definite than those in the susceptible line Mexican 142. The yield parameters seed yield and pods per plant, showed strong positive relationships.     

A model for estimating infection levels of anthracnose disease of mango

Anthracnose disease of mango caused by Colletotrichum gloeosporioides var. minor, spreads by water-borne conidia from vegetative parts of the tree to attack inflorescences and prevent fruit set. An analysis of data from laboratory studies demonstrated that infection by conidia during wet periods was related both to the temperature and to the duration of the wet period. A model was used to estimate infection levels of anthracnose disease in two mango orchards over three seasons. The number of infection periods recorded and the estimated percentage of conidia forming appressoria in these periods matched disease development during flush growth and flowering. In 1980, only two infection periods were detected during flowering in one of these orchards and blossom blight did not prevent fruit set. In 1981 and 1982 however, higher estimated levels of infection were recorded more frequently during the same time and severe blossom blight developed. A second orchard, situated in an area less favourable to disease, was also monitored during 1982. Nine infection periods were recorded during flowering in this orchard compared to 14 in the first. A moderate level of blossom blight developed in this orchard.     

Antioxidative enzymes and isozymes analysis of taro genotypes and their implications in <Emphasis Type="Italic">Phytophthora</Emphasis> blight disease resistance

Assessment of the differential expression of antioxidative enzymes and their isozymes, was done in 30 day-old ex vitro raised plants of three highly resistant (DP-25, Jhankri and Duradim) and one highly susceptible (N-118) genotypes of taro [Colocasia esculenta (L.) Schott]. Antioxidative enzymes were assayed in the ex vitro plants, 7 days after inoculation with the spores (15,000 spores ml⁻¹ water) of Phytophthora colocasiae Raciborski to induce taro leaf blight disease. Uninoculated ex vitro plants in each genotype were used as control. The activity of superoxide dismutase (SOD) and guaiacol peroxidase (GPX) increased under induced blight condition when compared with control. Increase in antioxidative enzymes was more (67–92%) in the resistant genotypes than that (21–29%) of the susceptible genotype. The zymograms of SOD and GPX in the resistant genotypes, with pathogenic infection, showed increased activity for anodal isoform of SOD and increased expression and/or induction of either POX 1 or POX 2 isoforms of GPX. In susceptible genotype, expression of the above isoforms was faint for SOD and nearly absent for GPX under both blight free and induced blight conditions. Induction and/or increased activity of particular isoform of SOD and GPX against infection of Phytophthora colocasiae in the resistant genotypes studied led to the apparent conclusion of linkage of isozyme expression with blight resistance in taro. This might be an important criterion in breeding of taro for Phytophthora leaf blight resistance.     

Area under disease progress curve and apparent infection rate of Alternaria blight disease of Indian mustard (Brassica juncea) at different plant age

Plant age has a major influence on the incidence of Alternaria blight disease in Indian mustard crops. Disease progression was monitored twice a week on the two chosen Indian mustard cultivars viz., Varuna and Rohini throughout the season. Severity of blight caused by Alternaria brassicae and Alternaria brassicicola decreased with delay in sowing. Calculation for A-value (Area under disease progress curve – AUDPC) and r-value (apparent infection rate) in crops sown on different dates could identify the speed of progress in the disease on leaves and pods, as the crop does not posses resistance to the pathogen till date. Thus, the probable dates of sowing enabling slow disease progress or the weather conditions coinciding with the different crop phenological stages demarcated the advantageous dates of sowing from the disadvantageous ones. However, cultivar Varuna is more susceptible as compared to the other cultivar Rohini, as apparent infection rate both on leaves and pods was higher in former. Highest per cent disease severity (PDS) for season highly correlated with date of sowing, i.e. delayed date of sowing increased PDS.     

Resistance in apple to shoot infection by Venturia inaequalis

Eight apple genotypes, including cultivars and breeding selections resistant and susceptible to Venturia inaequalis on foliage, were screened for shoot infection and the development of wood pustules following inoculation of shoot tips of 1–year maiden trees in the greenhouse. Where genotypes were highly resistant in terms of foliar symptoms (cvs Prima and Gavin), no shoot infection was observed. Where genotypes were highly susceptible in terms of foliar symptoms, then shoot tissue was either resistant (cv. Shinko) or susceptible (cv. Starking). In one experiment, shoot tips were inoculated sequentially as shoots extended. No pustules developed where inoculations were made later than May. In a further experiment, two leaf internode positions were inoculated on one occasion. Pustules were only observed where inoculations were made above the youngest unrolled leaf. The results suggested that shoot tips were more susceptible during early extension growth of the shoot. Pustules were noted in abundance on petioles of susceptible cultivars, and these probably contributed to early leaf abscission.     

Interaction between pod age and position on damage to cowpea Vigna unguiculata by hemipteran pod-sucking bugs

Laboratory and screenhouse studies were carried out to assess the relationship between pod age and pod position of cowpea and damage by different pod bug species. The coreids Clavigralla tomentosicollis St?l and Riptortus dentipes Fabricius caused significant damage to young pods of cultivated genotypes, in contrast to the coreid Anoplocnemis curvipes Fabricius and the pentatomid Aspavia armigera Fabricius which exhibited minor feeding activity. Percent seed damage declined with pod age, the critical stage for pod bug infestation being when pods were about eight days old. Clavigralla tomentosicollis and R. dentipes caused significantly higher damage to pods located within the leaf canopy, thus behaving differently from Anoplocnemis curvipes which showed a distinct preference for pods growing above the leaf canopy. The feeding activity of Aspavia armigera was not affected by the position of pods on the plant. Overall, the study suggests that cowpea genotypes with a short flowering period and pods held above the leaf canopy offer the most promise in the management of pod-sucking pests.