Leaf Rot Disease Research Articles

First Report of Lettuce Chlorotic Leaf Rot Disease Caused by Phytoplasma in China

Lettuce (Lactuca sativa) as annual or biennial crop is an important vegetable in China. The lettuce variety Feiqiao, which is extensively cultivated in autumn and winter, is grown for its stem and is a characteristic species bred in Yong'an City. Since October 2005, a new disease of lettuce has been observed sporadically in the fields. Initially, chlorotic symptoms, or a faded red color, were observed on the inner leaves of the infected lettuce plants. Then, the inner leaves bleached and appeared pale, while the top leaves became straight and elongated, and stopped growing. Gummosis was observed at the base of young leaves, and the whole plant became stunted and died. The disease was named lettuce chlorotic leaf rot disease. In 2008, there was a disease outbreak in Yong'an City with an incidence of approximately 30%. In 2012, total DNA was extracted from 0.1 g of leaf tissue collected from 20 symptomatic and five asymptomatic lettuce plants using the CTAB method. A PCR analysis was performed using the phytoplasma-specific primer set R16mF2/R16mR1 (1). An approximately 1.4-kb amplicon was obtained from all 20 symptomatic plants, but no corresponding DNA fragment was amplified from the five asymptomatic plants. PCR products were cloned in Escherichia coli DH5α, using the pMD18-T vector (TaKaRa, Japan), and two isolates were sequenced. The two 1,431-bp sequences were identical (GenBank Accession No. KJ668578). A BLAST analysis revealed a 99% identity between lettuce chlorotic leaf rot phytoplasma and mulberry dwarf phytoplasma, a group 16SrI phytoplasma described by Win et al. in 2012 (3). After analyzing with iPhyclassifier, the virtual RFLP pattern derived from the 16S rDNA F2n/R2 fragment was most similar to the reference pattern of the 16Sr group I, subgroup B (NC_005303), with a pattern similarity coefficient of 0.99 (2). Additionally, the leaf veins and roots with symptoms were processed for ultrastructural examinations using transmission electron microscopy. Many typical phytoplasma-like bodies were observed in the sieve elements in the leaf veins and roots, and they were spherical to oval or dumbbell shaped and 200 to 800 nm in diameter. In agreement with these findings, seven strains of phytoplasma from 16SrI-A and 16SrI-B subgroups were reported in association with lettuce plants exhibiting various types of symptoms which were not completely consistent with those observed in China (4). To our knowledge, this is the first report of a phytoplasma associated with lettuce in China.

First Report of Sclerotinia minor on Brassica rapa subsp. pekinensis in Central China.

Chinese cabbage (Brassica rapa subsp. pekinensis Hanelt) is a leafy vegetable widely grown in China. In December 2012 to March 2013, a leaf rot disease was observed on the lower part of cabbage leaves in a field in Xianning, Hubei Province, China, with the incidence of 6.3% in that field. The diseased leaves showed water-soaked rot and brown symptoms at the top surface. White fluffy mycelia and small black sclerotia were produced on the lesion surface. Cabbage leaf tissues from the disease/healthy-bordering areas and the sclerotia from the lesions were separately surface-sterilized in 75% ethanol (v/v) for 30 s, followed by rinsing three times in sterilized water. The surface-sterilized tissues and sclerotia were placed on potato dextrose agar (PDA) and incubated at 22°C. Individual emerging fungal colonies from the leaf tissue pieces and the sclerotia were transferred to new 9-cm-diameter PDA plates and incubated for 15 days. A total of 40 isolates (20 from diseased tissue and 20 from sclerotia) were obtained. All the isolates grew rapidly on PDA with an average growth rate of 2.2 cm/day and produced abundant sclerotia on the colony surface (1,179 sclerotia/plate on average). None of the isolates produced conidia and any other spores in the PDA cultures. Mature sclerotia were black, irregular, spherical or elliptical, had a diameter of 0.5 to 1 mm, and easily detached from the colonies. The cultural and morphological characteristics of the isolates matched the description for Sclerotinia minor Jagger (3). Two isolates, A1 (from leaf tissue) and S2 (from a sclerotium), were further identified by analysis of the ITS region (ITS1-5.8S rDNA-ITS2) using the primer pair ITS1/ITS4. The resulting 540-bp DNA sequences (GenBank Accession Nos. KC836493 for A1 and KC836494 for S2) shared 100% identity S. minor isolate 62907 (JF279880). Pathogenicity of the isolates A1 and S2 was tested by inoculating detached cabbage leaves with mycelial agar plugs removed from the colony margin of the 3-day-old cultures. Isolates A1 and S2 were each inoculated on three leaves with three plugs per leaf. Three cabbage leaves inoculated with PDA plugs were treated as a control. The treated leaves were covered with plastic films to maintain high humidity (>90% RH) and incubated at 22°C for 72 h under the regime of 12 h light/12 h dark. Results showed that while the control leaves remained healthy, brown and water-soaked lesions appeared around the mycelial agar plugs of each isolate. Average lesion diameters were 47.5 mm for A1 and 47.8 mm for S2. Abundant small sclerotia were produced on necrotic leaf lesions after 7 days. The fungus in diseased leaf tissues was re-isolated and the morphological characteristics of the resulting fungus were the same as S. minor isolated from infected field-grown cabbages. Therefore, S. minor is the causal agent for the leaf rot disease on Chinese cabbage. S. minor has been reported to infect a few plant species in the genus Brassica, including B. rapa subsp. oleifera (3), B. oleracea var. gemmifera (3), B. napus (2), B. oleracea var. capitata (3), B. oleracea var. botrytis (3), and B. rapa (3). It was found on B. rapa subsp. pekinensis in Korea (1). To our knowledge, this is the first report of S. minor on B. rapa subsp. pekinensis in China.

First Report of Myrothecium roridum Causing Leaf and Stem Rot Disease on Peperomia quadrangularis in Korea

In 2010, symptoms of leaf and stem rot were observed on potted plants (Peperomia quadrangularis) in a greenhouse in Yongin, Korea. The causative pathogen was identified as Myrothecium roridum based on morphological data, internal transcribed spacer sequence analysis, and pathogenicity test. To our knowledge, this is the first report of M. roridum causing leaf and stem rot disease on P. quadrangularis in Korea and elsewhere worldwide.

Rhizoctonia solani Identified as the Disease Causing Agent of Peanut Leaf Rot in China.

Peanut (Arachis hypogaea L.) is one of the most economically important oil crops in the world. Since the 1990s, the peanut industry has developed rapidly in China. However, because of the use of high-yield varieties and increased plant density, a peanut leaf rot disease occurred in Laixi Experimental Fields in Shandong Province, China in 2007. Leaves had nearly circular, brown lesions that enlarged quickly developing yellow-brown halos at the edges of the lesions. High relative humidity under field conditions led to complete necrosis of the leaves with cotton wool-like mycelia observed followed by the development of sclerotia on the leaf surface. Symptomatic plants were observed between 2007 and 2010, and symptomatic leaf tissue was collected from the Laixi Experimental Fields. An isolate (designated YF-1) from symptomatic peanut leaves was isolated and purified on potato dextrose agar (PDA) and water agar (WA) medium. On PDA, the colony appeared initially as colorless and grew to the diameter of a 9-cm petri dish within 3 days. As the mycelium aged, the colony color gradually became light brown, and sclerotia developed on the surface of the colony. YF-1 was identified as Rhizoctonia solani Kühn based on the number of nuclei per cell ranging from 4 to 13 (average 6.1), hyphal diameter being 7.5 to 12.9 μm (average 8.3 μm), branching at right angles, a septum was present near each hyphal branch with a slight constriction, and no clamp connection structures or conidia were ever observed (4). To further confirm the identity of isolate YF-1, genomic DNA was extracted using the DNeasy Plant Mini DNA Extraction Kit (Shanghai Leifeng Biotechnol. Co., Ltd.), and the complete internal transcribed spacer (ITS) region of ribosomal DNA was amplified and sequenced with a pair of primers ITS1/ITS4 (2). A GenBank BLAST search produced an exact match for the sequences of R. solani (AY154301), with 100% sequence similarity. To estimate the mode of anastomosis, YF-1 was paired on WA medium with each reference strain belonging to anastomosis groups (AGs) 1 through 8 (provided by Shandong Agriculture University) (1,3). The results indicated that YF-1 belonged to group AG-1, subgroup AG-1-IA of R. solani. Pathogenicity tests were conducted by inoculating 10 peanut leaves using a colonized paper disc method (filter paper 1 cm in diameter suspended in the mycelia suspension). Ten control leaves received paper discs without mycelium. Inoculated and non-inoculated plants were kept in humid chambers for 24 h at 25°C. Three days after inoculation, the leaves developed typical brown lesions that were similar to those of naturally diseased plants. Koch's postulates were fulfilled by reisolation of R. solani from symptomatic leaves. No symptoms were observed on control leaves. To our knowledge, this is the first report of peanut leaf rot caused by R. solani. Occurrence of the disease in China is a new threat to the health of peanut.

Appearance of a new leaf rot disease on common ice plant

An unknown disease abruptly appeared on hydroponic cultures of common ice plant (Mesembryanthemum crystallinum) in the greenhouse, causing catastrophic damage. Although the symptoms of the plant were unlike typical Botrytis lesions on leaves and stems of other plants, fungi isolated from the necrotic lesions on the plant were similar to genus Botrytis in terms of conidial shape, colony color and nature. A representative isolate, Ice-2, caused similar symptoms on the host plants after inoculation with conidia, and the same fungus was isolated from the lesions. The conidia and conidiophores of Ice-2 were morphologically similar to those of B. cinerea but not to those of B.allii, B. fabae or B. squamosa. The tested Botrytis fungi grew at temperatures between 5 and 30°C. Ice-2 grew faster than the others at the lower end of the temperature range. Ice-2 was also more virulent than B. cinerea (Bay-1) in artificial inoculations, especially on common ice plant leaves. The glyceraldehyde-3-phosphate dehydrogenase gene (G3PDH) sequence of Ice-2 was determined and compared with those from four Botrytis species. The gene sequence of Ice-2 appeared to be identical to that of B. cinerea. In leaf tests on common ice plant and kidney bean, the diseases caused by Ice-2 and Bay-1 were controlled equally well by the primary Botrytis fungicides. Based on the results of the present studies, Ice-2 is thought to be Botrytis cinerea Person: Fries.

Phytophthora nicotianae에 의한 아이비줄기썩음병

2007년 7월 전북 전주의 식물원에서 판매중인 아이비에서 줄기와 잎이 갈색으로 썩으며 급격히 말라죽는 증상으로부터 병원균을 분리 동정한 결과 Phytophthora nicotianae로 동정되었다. 병원균의 형태적 특성은 유두돌기가 있고 탈락성이 없는 난형의 유주자낭을 형성하였고, 크기는 평균 <TEX>$35.4{\times}25.2{\mu}m$</TEX>었고, 구형의 후막포자를 다량 형성하였으며, 크기는 평균 직경이 28.5 <TEX>${\mu}m$</TEX>였다. 유성생식형은 자웅이주로 A1 mating type이 관찰되었고 난포자의 크기는 평균 직경이 23.3 <TEX>${\mu}m$</TEX>였다. 균사의 생육적온은 <TEX>$25{\sim}30^{\circ}C$</TEX>였다. P. nicotianae에 의한 아이비줄기썩음병의 발생은 국내에서는 처음이다. A stem and leaf rot disease of English ivy(Hedera helix) was found in the flower market, Jeonju, Chonbuk province, Korea in July 2007. A Phytophthora species was isolated from the diseased part of the plant. Based on the mycological properties and pathogenesis the isolate was identified as Phytophthora nicotianae. The fungus produce ovoid sporangium which was ovoid to spherical which is noncaducous, papillate and averaged <TEX>$35.4{\times}25.2{\mu}m$</TEX> in dimension. Chlamydospores were abundantly produced on agar media and sized about 28.5 <TEX>${\mu}m$</TEX> in diameter. The fungus was heterothallic and A1 mating type. Oospores were measured 23.3 <TEX>${\mu}m$</TEX> in size. Optimum temperature for growth of the fungus was 25 to <TEX>$30^{\circ}C$</TEX>. Up to our knowledge, this is the first report demonstrating the stem rot on English ivy caused by P. nicotianae in Korea.

Pythium rot of figmarigold (Lampranthus spectabile) caused by Pythium aphanidermatum

A new leaf rot disease was found on the leaves of figmarigold (Lampranthus spectabile). The causal organism, identified as Pythium aphanidermatum was found to cause the same symptoms after artificial inoculation and was then reisolated from the inoculated plants. We propose to name the disease Pythium rot of figmarigold.

Incidence of leaf rot disease in relation to root (wilt) in young coconut palms and fungi in lamina and petiole lesions

Coconut leaf rot in association with root (wilt) is widespread in southern districts of Kerala, India. The disease complex has spread to northern districts of the state and also adjacent districts in Tamil Nadu. Where as the root (wilt) is a systemic infection (due to phytoplasma) the leaf rot is a foliar syndrome due to fungi (Colletotrichum gloeosporioides, Exserohilum rostratum, Fusarium spp.). Occurrence of leaf rot has been related to the incidence of root (wilt) and its appearance in young palms remained a matter of contention as to which disease precedes the other. Leaf rot lesions do occur on leaf petiole/mid-vein/mid-rib even as the disease lesions are known to be common on lamina (spindles). Investigations brought out that in majority of leaf rot affected young palms (2-5 years old) the flaccidity symptom of root (wilt) could be also discerned. In lesser number of affected palms, the other symptoms of root (wilt), yellowing and marginal necrosis, were also visible. As such, in 88.5% of leaf rot affected young palms one or the other symptom of root (wilt) has been recorded irrespective of season. C. gloeosporioides, E. rostratum and other fungi were found both in lamina and petiole lesions in different months. C. gloeosporioides was detected from petiole and lamina tissues in all the months, followed by E. rostratum, Fusarium spp. etc. C. gloeosporioides was isolated from these parts in more numbers and consistently during January-December. E. rostratum appeared erratically. Aggressiveness of C. gloeosporioides during months of wet season was confirmed. Fusarium spp. was isolated predominantly from these parts in dry months (January-May). Knowledge on occurrence of leaf rot in young palms in relation to root (wilt) and dynamics of leaf rot pathogens in leaf parts among months/seasons of year (in inoculums build-up, spread and dissemination) are important in the context of integrated management of root (wilt)-leaf rot complex.

CURATIVE AND PROPHYLACTIC CONTROL OF FUNGAL LEAF ROT COMPLEX IN ROOT (WILT) AFFECTED COCONUT PALMS IN INDIA

Root wilt disease (RWD) is a debilitating malady of coconut in India that is caused by phytoplasma. In RWD affected palms, leaf rot disease (LRD) is commonly superimposed. The LRD is due to fungi and this leaf rot phase forms an integral part of RWD complex. Control of LRD is important as it severely disfigures the palm and brings about rapid deterioration in its health and productivity. Control trial involving Phytosanitation of young leaves, pouring of broad spectrum - systemic fungicide, Contaf 5 E (Hexaconazole 5% EC) into the axil of spindle leaf besides a number of other measures was conducted to study their ameliorating effect on LRD. Prophylactic control trial, especially with the broad-spectrum fungicides was also conducted. Pouring of Contaf into the axil of spindles along with phytosanitory measures on the spindle and other young leaves significantly reduced the incidence of LRD in newly emerging spindles effecting cure. Application of the fungicide on RWD palms prior to the onset of LRD, offered prophylactic protection to emerging leaves against LRD. Relevance of practising integrated control measures, cure of LRD at an early stage itself, the need for strict adoption of crop management technology etc. for effective disease control are highlighted here.

IMPORTANT BIOCONTROL TRAITS OF MICROBIAL ANTAGONISTS OF LEAF ROT DISEASE OF COCONUT

Leaf rot disease of coconut, which occurs superimposed on root (wilt) disease of coconut in about 65 % of the cases, is an important disease prevalent in Kerala State of India. Colletotrichum gloeosporioides and Exserohilum rostratum are the main fungal pathogens of the disease, which disfigure the leaves and reduce yield substantially. Several biocontrol agents have been identified which reduce the disease development by these fungal pathogens. Pseudomonas spp. exhibit a host of mechanisms, which act in concert to bring about biocontrol activity. Bacillus spp. work mainly through production of antibiotics and other non-volatile metabolites. Mycoparasitism was the main contributing factor for actinomycetes group.

COCONUT LEAF ROT DISEASE COMPLEX A REVIEW

Occurrence of leaf rot disease (LRDC) of coconut is related to increased incidence of root wilt disease (RWD). The palms with RWD irrespective of age are susceptible, young ones are more susceptible to LRDC. Tender leaves especially the spindle play a critical role in LRDC incidence and the disease attributed to fungal complex. Among the 14 species of LRDC Angi, several were proved to be pathogenic; Colletotrichum gloeosporioides (Penzig) Penzig and Sacc and Exserohilum rostratum (Drechsler) Leonard and Suggs are discerned as the main pathogens. C. gloesporoides was aggressive during monsoons and positively correlated with rainfall and relative humidity (11% RH, whereas Erostratum less strongly correlated Fusarium spp. predominated in dry seasons. Importance of microclimate, survival and quiescence of the pathogens are to be determined. Diagnosis of RWD by techniques such as PCR and understanding the molecular basis of vulnerability of palms to LRDC would help to initiate early control measures. Planting of RWD cum LRDC resistantl tolerant varieties after eradicating the RWD infected palms is desirable. Protection ofyoung leaves by chemical or biocontrol agents or a combination of both with phytosanitation is important. 4 system approach with integrated measures needs to be utilizedfor sound management of LRDC.

Bacterial Leaf Rot of Odontioda Orchids Caused by Enterobacter cloacae.

An unknown disease causing leaf rot on leaves of Odontioda sp., which is an intergeneric hybrid of Odontoglossum, occurred in Tochigi Prefecture, Japan, during the summer of 1995. One species bacterium was almost purely isolated from the infected leaves. The isolated strains were pathogenic to Odontioda orchids in the dark with high temperature stress and high humidity. Based on results of API 20E strips and other physiological and biochemical tests, the strains were identified as Enterobacter cloacae (Jordan 1890) Hormaeche and Edwards 1960. They were also pathogenic to other orchids such as Calanthe discolor, C. furcata, Habenaria radiata, Miltonia sp. and Phaius minor f. punctaus, after inoculation and incubation for 2 days at 35°C. This is the first report of an orchid disease caused by E. cloacae, therefore, the name of “Bacterial leaf rot disease of Odontioda” was proposed.

Incidence of fungal species associated with leaf rot disease of coconut palms in relation to weather and the stage of lesion development

Summary.Leaf rot disease (LRD) of coconut occurs in Kerala State, India, and is generally severe during the monsoon, a time of high rainfall and r.h. and low maximum temperature. The pathogenic fungi Colletotrichum gloeosporioides, Exserohilum rostratum, Gliocladium vermoeseni, Fusarium solani, F. moniliforme var. intermedium, Thielaviopsis paradoxa and Rhizoctonia solani were among 14 species isolated from spindles of palms with LRD in multiple samplings of two experiments, each lasting 1 year. Co‐occurrence of fungi was observed in 70–76% of spindles although leaf pieces yielded mostly individual fungi irrespective of the stage of lesion development. C. gloeosporioides occurred most frequently on early lesions. The incidence of C. gloeosporioides was most strongly correlated with rainfall and r.h. and, negatively, with maximum temperature and hours of sunshine. It was the fungus isolated most commonly during the monsoon and occurred on early lesions more frequently than on advanced lesions (determined in one experiment). C. gloeosporioides is thus implicated as the principal pathogen involved in initiation of the disease during monsoons. Its relatively low incidence in the dry season suggests a quiescent phase between periods of parasitic activity. E. rostratum was isolated less frequently and its incidence was less strongly or consistently correlated with weather or with the stage of lesion development. Fusarium spp. and R. solani were associated with dryer weather and higher temperatures. The Fusarium spp. were the fungi isolated most commonly during part of the dry season (January‐March) and occurred more on early than on advanced lesions at one sample (January) when they may have been primary disease agents. R. solani was also more frequent on advanced lesions and may be principally a secondary coloniser of established lesions. The incidence of other fungi, which occurred less frequently and more sporadically, was not associated with weather or consistently with different stages of lesion development.

Studies on the Epidemiology of Leaf Rot and Leaf Spot Diseases of Betel Vine (&lt;i&gt;Piper Betle&lt;/i&gt; L.)

The experiment was conducted in an established pan betel vine crop field (Pan boroj). The disease data were recorded for 12 months. The incidence of leaf rot was observed in the month of June, July and August. The peak infection was noted in the second week of August, 2002 when the average temperature, relative humidly and rainfall were 29.60°C, 94.6% and 13.4mm respectively. The incidence of leaf spot was observed during months of March, April and May. But gradually infection reached maximum when average temperature, relative humidly and rainfall parameters were 26.7°C, 88.3% and 19.4mm respectively. The meteorological factor which had greatly influenced initiation of leaf spot was less favourable for leaf rot disease. Key words: Epidemiology; Betel vine; Leaf spot; Leaf rot diseases DOI: http://dx.doi.org/10.3329/bjsir.v46i4.9601 BJSIR 2011; 46(4): 519-522

Diseases of pan (Piper betle) in the central provinces

(1) A general account of the methods of pan cultivation practised in the Central Provinces and Berar is given. (2) A detailed account of the foot-rot diseases of pan caused byPhytophthora and a new species ofPythium, of the leaf-rot caused byPhytophthora and of the anthracnose disease caused byColletotrichum spp. is given. (3) A short account of the foot-rot diseases suspected to be caused bySclerotia Rolfsii, Rhizoctonia bataticola andR. Solani is given. (4) ThePhytophthora causing the foot-rot and leaf-rot disease is considered to beP. parasitica var.piperina, n. var. (5) ThePythium causing the foot-rot disease is namedP. piperinum n. sp. (6) Remedial measures for the control of the foot-rot, leaf-rot and anthracnose diseases are described.