Incidence Of Phytophthora Blight Research Articles

Seed biopriming or coating with rhizobacteria on hot pepper (Capsicum annuum L.): its effects on plant growth, yield, and incidence of Phytophthora blight

Seed biopriming or coating with rhizobacteria on hot pepper (<i>Capsicum annuum</i> L.): its effects on plant growth, yield, and incidence of Phytophthora blight

Bell Pepper (Capsicum annum L.) under Colored Shade Nets: Plant Growth and Physiological Responses

Use of colored shade nets has shown benefits in bell pepper and other horticultural crops. There is still, however, limited information on plant growth and physiology of bell pepper crop grown under colored shade nets. The objective was to determine the effects of colored shade nets on plant growth, leaf gas exchange, and leaf pigments of field-grown bell pepper. Experimental design was a randomized complete block with four replications and five shade treatments (black, red, silver, and white nets, and an uncovered control). Mean and maximal air temperature and midday root zone temperature (RZT) were highest in the unshaded treatment. Differences in air temperatures between shade net treatments were smaller compared with the differences in RZT between treatments. Plant fresh weight and stem diameter were reduced in the unshaded treatment, and there were no plant fresh weight and stem diameter differences among shade nets. The incidence of Phytophthora blight (caused by Phytophthora capsici) was greatest in the unshaded treatment. Leaf stomatal conductance (gS) and photosystem II efficiency were reduced and leaf temperature increased in unshaded conditions. Leaf net photosynthesis, gS, internal CO2, and PSII efficiency decreased with increasing leaf temperature. Differences in leaf temperature among shade net treatments were because of differences in solar radiation captured by leaves. Leaf total carotenoids were lowest in unshaded conditions and there were no differences in total carotenoids among the shade nets. Chlorophyll a concentration and chlorophyll a/b ratio was lowest in unshaded conditions. Leaf total phenols, flavonoids, and cupric reducing antioxidant capacity (CUPRAC) values were highest in red net and in unshaded conditions. Trolox equivalent antioxidant capacity (TEAC) values were highest in red net and lowest in silver net. In conclusion, compared with unshaded conditions, shade nets resulted in improved bell pepper plant growth and leaf gas exchange. These responses were due primarily to the reduced leaf and root zone temperatures under shaded conditions, regardless of the color of shade net. The differences in plant growth and function due to color of shade net were inconsistent or minor for most of the plant variables measured.

Bell Pepper (Capsicum annum L.) Crop as Affected by Shade Level: Fruit Yield, Quality, and Postharvest Attributes, and Incidence of Phytophthora Blight (caused by Phytophthora capsici Leon.)

High temperatures can be detrimental to bell pepper, resulting in reduced fruit yield and increased incidences of fruit disorders such as sunscald and blossom-end rot. Shade nets are used to modify the crop microenvironment to improve plant growth and yield. The objectives were to evaluate effects of shade level on fruit yield, quality, and postharvest attributes and the incidence of Phytophthora blight (caused by Phytophthora capsici Leon.) in bell pepper (Capsicum annum L.). Experiments were conducted in Tifton, GA, in 2008 (with cv. Heritage) and 2009 and 2010 (with cvs. Camelot, Lafayette, Sirius, and Stiletto). Bell pepper plants were grown under shade levels of 0% (unshaded, as a control), 30%, 47%, 63%, and 80%. Shade level affected fruit yield, quality, postharvest attributes, and incidence of Phytophthora blight in plants. Total marketable (Fancy and US1) fruit yield increased with increasing shade level to a maximum at 35% shade and then decreased with further increments in shade level. Relative to unshaded plants, marketable yields were improved by 119% (2008) and 43% (2009 and 2010) at 35% shade level. US2 and cull (sunscald) fruit number declined with increasing shade level. ‘Camelot’ produced among the greatest number and yield of marketable fruit; ‘Sirius’ had the heaviest fruit and greatest number of culls. Fruit nitrogen (N), phosphorus (P), and potassium (K) concentrations increased and aluminum (Al), molybdenum (Mo), and nickel (Ni) decreased with increasing shade level. ‘Lafayette’ had the highest fruit concentration of N, calcium (Ca), sulfur (S), manganese (Mn), and zinc (Zn). Fruit soluble solids and percent of fruit dry weight decreased with increasing shade level; fruit water loss rate and bacterial soft rot incidence were unaffected. Fruit skin a* and b* values decreased in yellow fruit cultivars (‘Lafayette’ and ‘Sirius’) with increased shade level. Incidences of Phytophthora blight in plants and fruit sunscald decreased with shade level. Beneficial effects of shading on bell pepper were associated with a reduction in irradiation, air temperature, and soil temperature under shaded conditions resulting in amelioration of heat stress in the plants. Optimal shade level for maximal fruit yield was that which maximized the cooling effect resulting from reduction of infrared (IR) radiation and minimized the decrease in net photosynthesis resulting from reduction in photosynthetically active radiation (PAR).

Effect of grafting on growth and incidence of phytophthora blight and bacterial wilt of pepper (Capsicum annuum L.)

This study was conducted to investigate the effect of grafting using commercial rootstocks and breeding lines on growth and resistance to both Phytophthora blight (Phytophthora capsici) and bacterial wilt (Ralstonia solanacearum), and to evaluate the breeding lines as candidates rootstocks for grafted peppers. Capsicum annuum ‘Nokkwang’ (scion) was grafted onto five commercial rootstocks (‘Kataguruma’, ‘Konesianhot’, ‘Koregon PR-380’, ‘PR-power’, and ‘Tantan’) and nine breeding lines (‘PR 901’, ‘PR 919’, ‘PR 920’, ‘PR 921’, ‘PR 922’, ‘PR 927’, ‘PR 928’, ‘PR 929’, and ‘PR 930’). Graft-take percentage was over 80% in all the grafted seedlings except those grafted onto ‘PR 901’ (75%). The number of leaves, stem diameter, leaf area, and dry weight of shoot of grafted seedlings were greater than those of non-grafted seedlings. Mineral contents in the shoots of grafted seedlings were significantly different, depending on rootstock genotypes. Marketable yield ranged from 1.35 to 1.96 kg per plant depending on rootstock genotypes, and was highest in peppers grafted onto ‘PR 901’ (1.95 kg) and non-grafted peppers (1.96 kg), and lowest in those grafted onto ‘PR 928’ (1.35 kg). Gross yield was highest in peppers grafted onto ‘Konesianhot’ (2.64 kg). Among nine breeding lines, three rootstocks (‘PR 920’, ‘PR 921’, and ‘PR 922’) were selected as candidate rootstocks for the grafted pepper based on graft-take, growth, yield, fruit quality, and resistance to diseases. Three major pepper cultivars (‘Nokkwang’, ‘Saengsaeng Matkkwari’, and ‘Shinhong’) were grafted onto those three breeding lines and ‘Tantan’ (control). Peppers grafted onto breeding lines of ‘PR 920’, ‘PR 921’, and ‘PR 922’ showed greater resistance to both Phytophthora blight and bacterial wilt without the decrease in yield and fruit quality. Accordingly, they were considered to be used as rootstocks resistant to both Phytophthora blight and bacterial wilt for pepper production.

Xenorhabdus nematophilla 유래물질 벤질리덴아세톤의 고추 병해 방제 효과

벤질리덴아세톤은 모노테르펜 화합물로 곤충병원세균인 Xenorhabdus nematophilla K1의 대사물질이다. 본 연구는 벤질리덴아세톤을 이용하여 고추의 두 가지 주요 병해에 대한 방제 가능성이 조사되었다. 벤질리덴아세톤은 역병균 Phytophthora capsici와 탄저병균 Colletotrichum acutatum에 대해 강력한 억제능력을 가지고 있었다. 이러한 벤질리덴아세톤의 항균력은 태양이 비치는 자연조건에서 60일 이상 유지되었으며, 토양수 내에서도 상실되지 않았다. 벤질리덴아세톤을 혼합한 토양에 심겨진 고추 근권토양에 Phytophthora capsici 현탁액을 관주하였을 때, 역병 발생이 크게 감소되었다. 또한 Colletotrichum acutatum에 오염된 고추 열매 표면에 벤질리덴아세톤 용액을 살포하여 탄저병 발생을 억제할 수 있었다. 이러한 결과는 벤질리덴아세톤을 고추 역병과 탄저병 방제용 농약으로 개발할 수 있음을 제시하고 있다. A monoterpenoid benzylideneacetone (BZA) is a bacterial metabolite isolated from culture broth of an entomopathogenic bacterium, Xenorhabdus nematophila K1. It was tested in this study the control efficacy of the metabolite against two major fungal diseases occurring in red-pepper plants. BZA exhibited significant antifungal activities against Phytophthora capsici and Colletotrichum acutatum. Under natural light conditions, the antifungal activity of BZA was maintained for more than sixty days. The antifungal activity of BZA was not lost even in soil because the incidence of Phytophthora blight against red-pepper plants was significantly reduced when the suspensions of P. capsici were poured to the rhizosphere soils mixed with BZA. Application of the BZA suspension spray to the fruit surface infected with C. acutatum significantly suppressed the disease occurrence of anthracnose on the red-pepper plants. These results suggest that BZA can be used to develop a promising agrochemical to control phytophthora blight and anthracnose of redpepper plants.

비닐터널 유인재배가 고추 역병과 탄저병의 발생에 미치는 효과

노지피복 재배포장과 비닐터널유인 재배포장의 재배양식별 고추 탄저병과 역병의 발생정도를 조사하였다. 비닐터널유인재배포장의 초기 생육이 노지피복재배포장(관행)보다 월등히 우세하였다. 재배 양식별 고추 주요 병해인 탄저병과 역병의 발생정도를 조사한 결과 노지피복재배포장에 비해 터널유인 재배한 포장에서 역병발생은 60.3%, 탄저병발생은 26.9% 경감효과가 있었다. 재배양식별 건과 수확량을 조사한 결과 노지피복 재배포장대비 48.5%가 많은 것으로 조사되었다. This survey was conducted to investigate effect of covering with polyvinyl (<TEX>$120{\times}90cm$</TEX>) on incidence of Phytophthora blight and anthracnose and growth. Early growth of pepper plant was superior when was covered with polyvinyl after planting. Incidence of anthracnose and Phytophthora blight was lower 26.9% and 60.3% in covering system than those in conventional culture system, respectively. A yield of dried red pepper was more 48.5% in cultured with covering system than that in conventional culture system.

Fitness of Isolates of Phytophthora capsici Resistant to Mefenoxam from Squash and Pepper Fields in North Carolina.

Despite the wide adoption of mefenoxam (Ridomil Gold EC) for vegetables in North Carolina, the incidence of Phytophthora blight on pepper (Capsicum annuum) and squash (Cucurbita pepo) is high. Seventy-five isolates of Phytophthora capsici were collected in five pepper and one squash field in order to assess mefenoxam sensitivity. The relative fitness of resistant and sensitive isolates was contrasted in vitro by their respective rates of colony growth and their ability to produce sporangia in unamended V8 juice agar medium. In in vivo experiments, the aggressiveness of isolates on pepper was evaluated. The frequency of resistant isolates in North Carolina populations was 63%, considerably higher than resistance levels in areas where mefenoxam is not widely adopted. Resistant isolates grew on amended media at rates >80 to 90% and >100% of the nonamended control at 100 μg ml-1 and 5 μg ml-1, respectively. Sensitive isolates did not growth at 5 or 100 μg ml-1. All isolates from three fields, including two pepper and a squash field, were resistant to mefenoxam. Populations from other fields were composed of either mixes of sensitive and resistant isolates or only sensitive isolates. Response to mefenoxam remained stable during the course of in vitro and in planta experiments. Occurrence of a mefenoxam-resistant population of P. capsici on squash is reported here for the first time in North Carolina. When measured by rate of colony growth, sporulation in vitro, or aggressiveness in planta, fitness of resistant isolates was not reduced. Mefenoxam-resistant isolates from squash were as aggressive on pepper as sensitive or resistant pepper isolates. These results suggest that mefenoxam-resistant populations of P. capsici are as virulent and fit as sensitive populations.

Phytophthora Blight and Dieback in North Carolina Nurseries During a 2003 Survey.

A survey of 14 nurseries growing hybrid rhododendron, Pieris spp., or Viburnum spp. was conducted as part of the 2003 Sudden Oak Death Pilot National Survey to determine if Phytophthora ramorum, the causal agent of sudden oak death, had been introduced to nurseries in North Carolina. Over 220,000 hybrid rhododendrons, 1,700 plants of Pieris spp., and 2,800 plants of Viburnum spp. were surveyed. Across nurseries, blight and dieback incidence averaged 2.4% for Pieris spp. and 10% for rhododendron. P. ramorum was not recovered by isolation or detected by polymerase chain reaction in the 347 plant samples collected. Three species of Phytophthora were isolated from hybrid rhododendron and Pieris spp., but no Phytophthora isolates were recovered from Viburnum spp. P. citricola and P. cambivora were isolated most frequently (61 and 39 isolates, respectively), while 2 isolates of P. cactorum were recovered. Occasionally, two Phytophthora spp. were found in the same block of rhododendrons within a nursery, but only one species was recovered from an individual plant. Most cultivars of rhododendron surveyed, including 'English Roseum,' 'Nova Zembla,' and 'Roseum Elegans,' had less than 0.5% incidence of Phytophthora blight and dieback, whereas 'Lee's Dark Purple' had 3.8% disease incidence across all nurseries surveyed.

Effect of urban plant debris and soil management practices on plant parasitic nematodes, Phytophthora blight and Pythium root rot of bell pepper

Soil management practices were examined for their effects on plant parasitic nematodes and soilborne diseases of field grown bell pepper ( Capsicum annuum). Field plots were established on a diversified organic vegetable farm that had been under certification for 5 years and on a conventional pepper farm that had been fumigated with methyl bromide/chloropicrin and cropped annually to bell pepper for 25 years. The plot design was a split plot where the main treatment was the application of 67 t ha −1 of urban plant debris (UPD), and sub plots were; (1) no-till production into residue remaining from a cover crop of Sunn Hemp ( Crotalaria juncea), (2) or Iron-clay Pea ( Vigna unguiculata), (3) creation of raised polyethylene-mulched beds and, (4) soil solarization for a 6–8 week period. Soil fumigation with methyl bromide/chloropicrin (67/33) was evaluated only at the conventional farm site. Experiments were conducted in 1999 and repeated in 2000. At the organic farm only Pythium root rot was identified whereas, at the conventional farm Phytophthora blight was the predominant soilborne disease. UPD application significantly reduced the incidence of Pythium root rot from 24.7% to 12.1% in 2000 at the organic site and the incidence of Phytophthora blight from 49.8% to 31.1% in 1999 at the conventional site. At the conventional site, Phytophthora blight was significantly lower in solarized (21.9%) and fumigated (22.1%) plots when compared to plots with untreated soil covered by polyethylene mulch (46.1%) in 1999. In 2000, Phytophthora blight was significantly higher in the no-till treatments (91.1–91.8%) when compared to the other soil management treatments (50.2–63.5%). UPD application significantly reduced the populations of plant parasitic nematodes from 64.5 to 37.5 per 100 cm 3 soil in 2000 at the organic site and from 94.3 to 12.9 in 1999 at the conventional site, when compared to treatments not receiving UPD. At the organic site the populations of plant parasitic nematodes were significantly higher in the no-till Sunn Hemp plots than solarized plots. At the conventional site, significantly higher populations of Meloidogyne spp. were found in solarized and no-till Sunn Hemp treatments then in untreated soil covered with plastic mulch, while significant reductions in Meloidogyne spp. only occurred with soil fumigation. The results demonstrate that several nonchemical management practices can reduce the impact of soilborne pests for fresh market bell pepper production in a humid, subtropical climate.

Incidence of Phytophthora Blight and Verticillium Wilt Within Chile Pepper Fields in New Mexico.

Statewide surveys of commercial chile pepper (Capsicum annuum) fields were conducted in New Mexico from 2002 to 2004 to gain information on the incidence of diseases with wilt symptoms and their causative agents. Fifty-nine fields were surveyed during the course of this 3-year study when chile pepper plants were at growth stages from green fruit to beginning red fruit. All fields were affected by diseases with wilt symptoms. The proportion of total field area exhibiting symptoms of wilt spanned from less than 1% to over 80%. Field diagnostics along with laboratory assays of wilted plants revealed that the wilting was caused by Phytophthora capsici and Verticillium dahliae. The two pathogens were both found in 80% of the fields, and occurred together in some wilted plants in 12% of the fields. Average incidence of plant infection (number of plants infected with P. capsici or V. dahliae out of 5 to 25 wilted plants sampled) varied from approximately 40 to 90% for P. capsici, and from 18 to 65% for V. dahliae. Incidence of plant infection by P. capsici was approximately 40% less in fields with drip irrigation than in fields with furrow irrigation. In contrast, incidence of plant infection by V. dahliae was approximately 32% greater under drip irrigation than under furrow irrigation. In pathogenicity tests, isolates of P. capsici and V. dahliae caused symptoms in inoculated chile pepper identical to those in field-grown chile pepper plants. Results indicate that diseases with wilt symptoms are well established in chile pepper production fields, with P. capsici and V. dahliae posing the most serious challenge to chile pepper producers in New Mexico.

Root Colonizing and Biocontrol Competency of Serratia plymuthica A21-4 against Phytophthora Blight of Pepper

The biocontrol agent Serratia plymuthica A21-4 readily colonized on the root of pepper plant and the bacterium moves to newly emerging roots continuously. The colonization of A21-4 on the pepper root was influenced by the presence ofPhytophthora capsici in the soil. When P. capsici was introduced in advance, the population density of A21-4 on the root of pepper plant was sustained more than cfu/g root until 3 weeks after transplanting. On the other hand, in the absence of P. capsici, the population density of A21-4 was reduced continuously and less than cfu/g root at 21 days after transplanting. S. plymuthica A21-4 inhibited successfully the P. capsici population in pepper root and rhizosphere soil. In the rhizosphere soil, the population density of P. capsici was not increased more than original inoculum density when A21-4 was treated, but it increased rapidly in non-treated control. Similarly, the population density of P. capsici sharply increased in the non-treated control, however the population of P. capsici in A21-4 treated plant was not increased in pepper roots. The incidence of Phytophthora blight on pepper treated with A21-4 was 12.6%, while that of non-treated pepper was 74.5% in GSNU experimental farm experiment. And in farmer`s vinyl house experiment, the incidence of the disease treated with the fungicide was 27.3%, but treatment of A21-4 resulted in only 4.7% of the disease incidence, showing above 80% disease control efficacy.

Phytophthora Blight: A Serious Threat to Cucurbit Industries.

Introduction Phytophthora blight, caused by the oomycete Phytophthora capsici, has become one of the most serious threats to production of cucurbits and peppers, both in the United States and worldwide (2,6,8,9,11,17,18,22,27,30). Phytophthora capsici was first described by Leonian on pepper in New Mexico in 1922 (20). In 1931, Tucker (38) classified it as a species of the genus Phytophthora and considered P. capsici as a host-specific fungus pathogenic on pepper. Subsequently, taxonomists (23,36,37) studied Phytophthora isolates from various hosts in the world and re-described the taxonomy of P. capsici. Recently, the incidence of Phytophthora blight on cucurbits has dramatically increased in Illinois (2,32) and other cucurbit-growing areas in the world (8,9,17,18), causing up to 100% yield loss. Cucurbit industries, particularly processing industries, are seriously threatened by heavy crop loss resulting from Phytophthora blight. For example, outbreaks of Phytophthora blight have threatened the processing pumpkin and other cucurbit industries in Illinois, where 90% of processing pumpkins produced in the US are grown (2,3) (Figs. 1 and 2). Similarly, the pickling cucumber industry of Michigan is jeopardized by the increased occurrence of Phytophthora blight (8). Because of heavy crop losses the growers often have to abandon their own farms for cucurbit production and move into different areas, sometimes traveling more than 50 miles, to find fields not infested with P. capsici.

Resistance to Mefenoxam and Metalaxyl Among Field Isolates of Phytophthora capsici Causing Phytophthora Blight of Bell Pepper.

Incidence of Phytophthora blight in bell pepper fields that were sprayed for the first time with Ridomil Gold (mefenoxam) according to labeled recommendations was higher in North Carolina in 1997 than in previous years. Mefenoxam is the more active enantiomer contained in the racemic fungicide metalaxyl. A total of 150 isolates were obtained from 17 fields at eight grower locations. Among isolates from all locations, 30% were classified as sensitive, 10% as intermediate, and 59% were resistant to mefenoxam. Mefenoxam-resistant isolates were found in 82% of the fields sampled (14 of 17 fields). The proportion of resistant isolates in individual (fields ranged from 28 to 100%. The mean effective concentration (EC50) values for mefenoxam-sensitive isolates was 0.568 μg ml-1 (ranging from 0.12 to 1.1 μg ml-1), whereas the mean EC50 value for mefenoxam-resistant isolates was 366.5 μg ml-1 (ranging from 3 to 863 μg ml-1). The mean EC50 value for metalaxyl-sensitive isolates was 0.27 μg ml-1 (ranging from 0.00002 to 1.3 μg ml-1) and for metalaxyl-resistant isolates was 470.34 μg ml-1 (ranging from 10 to 966 μg ml-1). The greatest proportion of resistant isolates came from fields where mefenoxam was used alone rather than in combination with other fungicides. Both mating types were found among resistant isolates, suggesting that these isolates may persist in soil in subsequent years. Field isolates of Phytophthora capsici resistant to mefenoxam on pepper have not been reported previously and now pose new challenges for management of this important disease.