Genetic variability in mulberry against Myrothecium leaf spot (Myrothecium roridum) and identification of resistance genotypes

Disease response of 30 mulberry genotypes to Myrothecium leaf spot (Myrothecium roridum) was studied under inoculated condition. It was observed that 10 genotypes were resistant, 16 genotypes moderately resistant and 4 genotypes moderately susceptible to the disease. Area under disease progress curve (AUDPC) and apparent infection rate was found significantly lower in the resistant genotypes. Correlation study revealed that percent disease index (PDI) has significant positive correlation with AUDPC and apparent infection rate. Genetic analysis of disease-resistant traits (PDI and mean AUDPC) revealed that phenotypic coefficient of variation (PCV) was higher than genotypic coefficient of variation (GCV) for both PDI and AUDPC, and GCV/PCV ratio was also found high which indicated that disease-resistant traits to Myrothecium leaf spot were not much influenced by environment. High heritability coupled with high genetic advance indicated that the disease-resistant traits are due to additive gene effect thereby indicating the amenability of disease-resistant in the selection process. Hence disease-resistant mulberry genotypes viz. C-763, S-34, Jodhpur, Cyprus, Australian and Hungarian may be used as source of resistance to Myrothecium leaf spot for future breeding programme. Besides, high yielding genotypes viz. Tr-10, C-763 and S-34 may be recommended for commercial exploitation     

Screening of chilli germplasm for resistance to Alternaria leaf spot disease

Chilli is one of the spices used to enhance the flavour and taste of cooked food. Fungal diseases are the main biological constraints in chilli production, and Alternaria leaf spot disease caused by Alternaria alternata is one of the most devastating diseases of chilli. One of the effective and environmentally friendly ways to control this disease is introgress resistance from wild relative/varieties to the cultivated one. The first step towards introgression of resistance genes is to screen the chill germplasm for leaf spot resistance. In the current study, we screened the chilly germplasm and identified the sources of leaf spot resistance, which can be harnessed in resistance breeding programmes.     

Association of morphological and biochemical features of mulberry lines with resistance to bacterial leaf spot

Xanthomonas campestris pv. mori causes bacterial leaf spot (BLS) of mulberry (Morus spp.) worldwide. Twenty mulberry lines with contrasting response to BLS showed significant (p?<?0.01) variation between resistant and susceptible groups for stomata frequency (SF), trichome density (TD), total soluble sugar (TSS) and polyphenol (PP) content, while non-significant for chlorophyll content. Heritability (broad-sense) estimates obtained from the variance component analysis were high (≥0.72) for these traits. The disease severity index values of the lines were significantly negatively correlated with TD (r?=??0.66; p?<?0.01), TSS (r?=??0.73; p?<?0.01) and PP (r?=??0.61; p?<?0.01), while positively correlated with SF (r?=?0.65; p?<?0.01). The cluster analysis was based on highly significant four variables and DSI values, and classified the lines into two major clusters. The resistant lines that come under cluster-I had high TD, TSS and PP, while those in susceptible category had high SF in cluster-II. These findings suggest that direct selection for SF, TD, TSS and PP will be effective for development of host resistance against BLS in mulberry.     

Response of mulberry accessions to major foliar diseases in temperate conditions of Jammu and Kashmir,India

Thirty-three indigenous and 24 exotic mulberry accessions belonging to five Morus spp. originated from seven countries distributed in temperate and tropical climates were observed for their response to two major foliar diseases during 2010 and 2011 under temperate conditions of Jammu and Kashmir, India. Leaf spot and powdery mildew severity (Percent Disease Index (PDI)) ranged from 0.00 to 74.90% and 0.00 to 59.85%, respectively. Indigenous and exotic accessions responded similarly to leaf spot, but varied too much to powdery mildew. Irrespective of origin, response in ascending order of PDI for leaf spot is M. multicaulis, M. indica, M. alba, M. kayayama and M. bombycis and for powdery mildew is M. multicaulis, M. kayayama, M. bombycis M. alba and M. indica. Among indigenous accessions, Brentul Kashmir offered highest resistance to both the diseases. Nadigam offered maximum resistance only to leaf spot followed by Himachal local; while Chinarpati followed by Mysore local only for powdery mildew. Among exotic accessions, Ichinose offered maximum resistance to both the diseases followed by Kokusou-21 and Tagowase.     

苦瓜叶片结构与白粉病抗性的关系

以不同抗白粉病的苦瓜品系幼苗为材料,对它们的叶片及上下表皮厚度、栅栏组织及海绵组织厚度、叶片结构紧密度及疏松度、蜡质含量、比叶重、气孔及茸毛密度等叶片结构进行观察比较,探讨苦瓜白粉病抗性与其主要叶片结构指标的关系。结果显示:（1）抗病苦瓜品系叶片的蜡质含量显著高于感病品系,与病情指数呈显著负相关关系,蜡质层是其抵抗和延迟病原菌侵入的一个有力结构屏障。（2）感病品系叶片的气孔和叶背面茸毛数量显著多于抗病品系,且叶背面的气孔及茸毛密度与病情指数呈显著正相关关系,即气孔和茸毛越少越抗病。（3）抗病苦瓜品系的叶片栅栏组织以及海绵组织排列整齐、紧密,而高感品系的叶片组织出现大量孔隙,较难观察到完整细胞。（4）抗病品系叶片厚度、下表皮厚度、栅栏组织厚度、叶片结构紧密度明显高于感病品系,而感病品系的海绵组织厚度、叶片结构疏松度明显高于抗病品系;且苦瓜比叶重与其白粉病抗性关系不大。研究认为,苦瓜叶片蜡质含量、叶背面气孔及茸毛密度可以作为苦瓜白粉病抗性鉴定的参考指标。     

Loss of actin cytoskeletal function and EDS1 activity,in combination,severely compromises non-host resistance in Arabidopsis against wheat powdery mildew

Plant immunity against the majority of the microbial pathogens is conveyed by a phenomenon known as non-host resistance (NHR). This defence mechanism affords durable protection to plant species against given species of phytopathogens. We investigated the genetic basis of NHR in Arabidopsis against the wheat powdery mildew fungus Blumeria graminis f. sp. tritici (Bgt). Both primary and appressorial germ tubes were produced from individual Bgt conidia on the surface of the Arabidopsis leaves. Attempted infection occasionally resulted in successful penetration, which led to the development of an abnormal unilateral haustorium. Inoculation of a series of Arabidopsis defence-related mutants with Bgt resulted in the attenuation of reactive oxygen intermediate (ROI) production and salicylic acid (SA)-dependent defence gene expression in eds1, pad4 and nahG plants, which are known to be defective in some aspects of host resistance. Furthermore, Bgt often developed bilateral haustoria in the mutant Arabidopsis lines that closely resembled those formed in wheat. A similar decrease in NHR was observed following treatment of the wild-type Arabidopsis plants with cytochalasin E, an inhibitor of actin microfilament polymerisation. In eds1 mutants, inhibition of actin polymerisation severely compromised NHR in Arabidopsis against Bgt. This permitted completion of the Bgt infection cycle on these plants. Therefore, actin cytoskeletal function and EDS1 activity, in combination, are major contributors to NHR in Arabidopsis against wheat powdery mildew.     

Pathogenesis of mulberry leaf spot in response to meteorological aspects of Kashmir,India

In this study, the influence of climatic factors on the development of leaf spot diseases of mulberry (Morus alba L.) in Kashmir, India was studied. It was found that the highest disease incidence and severity of Goshoerami variety was found in tree type (13.86% and 1.98%) followed by dwarf (7.53% and 1.67%) and bush (3.38% and 0.99%), respectively. Due to infection of pathogen, the relative water content and chlorophyll content of leaves were consistently decreased. The order of reduction in relative water content of infected leaves was found as: bush?>?dwarf?>?tree, while as the reduction in chlorophyll content: bush?>?tree?>?dwarf. It was also found that temperature of 25–30?°C and relative humidity of above 80% favoured the development of the disease. Rapid development of disease was found during the month of June, July and August when average temperature and relative humidity was about 25–30°C and 80%, respectively.     

Characterization of Fusarium spp. associated with pineapple fruit rot and leaf spot in Peninsular Malaysia

Pineapple (Ananas comosus) is one the important fruit crops planted in Malaysia, and this study was conducted to determine Fusarium spp. associated with diseases of the fruit crop as Fusarium is prevalent in tropical countries. Our objective was to identify and characterize Fusarium spp. associated with pineapple fruit rot and leaf spot mainly found on the fruits and leaves in Peninsular Malaysia. Fusarium isolates (n = 108) associated with pineapple fruit rot and leaf spot were characterized by morphological, molecular and phylogenetic analyses, a mating study and pathogenicity testing. TEF‐1α sequence analysis identified Fusarium proliferatum, Fusarium verticillioides, Fusarium sacchari and Fusarium sp. Mating was successful only between tester strains of F. proliferatum and F. verticillioides. Sexual crosses with standard tester strains showed that 82 isolates of F. proliferatum produced fertile crosses with mating population D (Gibberella intermedia) and three isolates of F. verticillioides were fertile with the tester strain of mating population A (Gibberella moniliformis). All isolates were pathogenic, causing pineapple fruit rot and leaf spot, thus fulfilling Koch's postulates.     

Identification of resistance source in wheat germplasm against spot blotch disease caused by Bipolaris sorokiniana

Four hundred and twenty-two spring wheat germplasm (Triticum aestivum L.) lines belonging to Indian, CIMMYT and Chinese wheat programme were evaluated for their tolerance against natural epiphytotic conditions of spot blotch caused by Bipolaris sorokiniana at the hot spot location, Pusa, Bihar, India. Of the 422 entries screened, none of the genotype showed immunity to the disease, whereas 52 were resistant, 180 moderately susceptible, 171 susceptible and 19 highly susceptible. Indian germplasm lines tended to be more susceptible than lines originated from CIMMYT and China. Chirya 3, Chirya 7 and Mayoor from CIMMYT showed high degree of resistance to the disease both under field and polyhouse conditions. On the basis of the disease severity under field conditions, 20 promising resistant genotypes and 10 highly susceptible lines were isolated for further testing under artificial epiphytotic conditions in polyhouse for genetic analysis and their potential for spot blotch resistance breeding.     

Alternaria alternata f.sp. cucurbitae, the cause of a new leaf spot disease of melon (Cucumis melo)

A leaf spot disease of melon caused by Alternaria alternata f.sp. cucurbitae was recorded for the first time in Crete. Necrotic flecks surrounded by chlorotic halos developed on the cotyledons and the leaves of the middle and the upper part of the plants; the flecks enlarged and coalesced to form lesions of 2 cm or more in diameter with brown fructifications of the pathogen on their surface. Severely affected cotyledons and leaves became chlorotic and died. Of 16 species from eight botanical families that were inoculated, only those of the Cucurbitaceae were susceptible. Of four isolates of A. alternata from tomato, sunflower, pear and cucumber, only the cucumber isolate was pathogenic to melon foliage.     

Forecasting model of bacterial leaf spot disease of mulberry caused by Xanthomonas campestris pv. mori

In order to develop weather-based forecasting model of bacterial leaf spot (BLS) disease of mulberry caused by Xanthomonas campestris pv. mori, weekly disease severity data were recorded for three years on the ruling cultivar S-1. Daily meteorological data viz. maximum temperature, minimum temperature, maximum relative humidity, minimum relative humidity, rainfall and number of rainy days were also recorded. It was observed that BLS appeared in April/May and continued up to November with maximum severity in July. The correlation coefficient between disease severity and meteorological parameters revealed that the BLS disease severity has significant positive correlation with minimum temperatures, maximum and minimum relative humidity, rainfall and number of rainy days and negative correlation with maximum temperature. Multiple regressions analysis revealed that average of maximum temperature, minimum temperature and rainfall of preceding seven days and maximum relative humidity, minimum relative humidity of previous 9–15 days was found to maximally influence BLS disease severity. The contribution of the meteorological factors was found to be highest of minimum temperature (40.65%) followed by maximum temperature (24.20%), maximum relative humidity (16.41%), minimum relative humidity (8.07%), rainfall (5.29%) and number of rainy days (5.38%).     

Morphological and molecular characterization of Diplodia seriata,the causal agent of canker and twig dieback disease on mulberry in Iran

Mulberries are cultivated for different purposes: for feeding larvae of silkworm, Bombyx mori, as fresh and dry food resources, in wood instrument industry, in pharmaceutical industry and as outdoor ornamental trees in Iran. In recent years, twig and branch canker disease symptoms have been noticed on mulberry trees in northwestern parts of Iran. Diplodia isolates were repeatedly recovered from symptomatic tissues. Based on cultural and morphological features, the isolates were identified as Diplodia seriata. The identity of the isolates was further confirmed using sequence data from internal transcribed spacer (ITS)-rDNA and ef-1α gene. A phylogenetic analysis using ITS sequence data clustered the isolates obtained in this study together with known Diplodia seriata isolates of other woody hosts from GenBank. Inoculation studies carried out on white mulberry twigs using an excised shoot method revealed that the isolates are pathogenic on this host. D. seriata have been reported from other woody host plant species such as Juglans nigra and Vitis vinifera in Iran, however, to the best of our knowledge, the occurrence of D. seriata on mulberry trees is new for Iran. The distribution and reaction of different Morus spp. to D. seriata remain to be studied.     

与小麦白粉病抗性基因Pm2紧密连锁RAPD标记的筛选研究

以２５６个随机引物对含小麦抗白粉病基因Ｐｍ２近等基因系进行ＲＡＰＤ分析,发现１７个随机引物的扩增产物在抗、感ＮＩＬｓ材料间表现多态性,且其中５个引物经４次以上重复,均获相同结果,其多态性标记分别为ＯＰＭ０８(１６００)、ＯＰＩ０４(１７００)、ＯＰＨ１９(１１００、ＯＰＥ０９(９００)及ＯＰＭ１６(８５０)。当以这５个随机引物对１４个已知含Ｐｍ２基因的抗病材料及９个不含Ｐｍ２基因的感病材料进行检测时,只有标记ＯＰＩ０４(１７００)在１２个抗病材料中出现（另两个抗病材料中未检测到）,而在９个感病材料中均未出现。进一步用 ＯＰI(０４)对１０２株（Ｃｈａｎｃｅｌｌｏｒｘ Ｕｋａ／８＊Ｃｃ）Ｆ２分离群体进行分析,估算出标记ＯＰＩ０４(１７００)与Ｐｍ２基因间的遗传距离为１２．２±３．３ｃＭ。     

Acibenzolar-S-methyl-Induced Systemic Resistance against Anthracnose and Powdery Mildew Diseases on Cucumber Plants without Accumulation of Phytoalexins

In a study to elucidate the possible involvement of phytoalexins in acibenzolar-S-methyl (ASM)-induced systemic resistance in cucumber plants ( Cucumis sativus L.), the phenolic compounds were extracted from ASM-treated and inoculated plants and compared with those from Milsana^®-treated plants previously reported to accumulate phytoalexins in cucumber. The glycoside-linked phenolic compounds from cucumber leaves were tested for their antifungal activity to the growth of pathogens which were most effective against the cucumber anthracnose fungus Colletotrichum orbiculare , followed by the scab fungus Cladosporium cucumerinum but ineffective against the Corynespora leaf spot fungus Corynespora cassiicola . Nevertheless, the accumulations of active compounds appeared to increase with the growth stages of cucumber plants irrespective of ASM treatment. In ASM-pretreated cucumber plants either inoculated with anthracnose or the powdery mildew fungus, there was no increase in phytoalexin-like phenolics.     

Identification of powdery mildew (Erysiphe graminis sp. tritici) and take-all disease (Gaeumannomyces graminis sp. tritici) in wheat (Triticum aestivum L.) by means of leaf reflectance measurements

The ability to identify diseases in an early infection stage and to accurately quantify the severity of infection is crucial in plant disease assessment and management. A greenhouse study was conducted to assess changes in leaf spectral reflectance of wheat plants during infection by powdery mildew and take-all disease to evaluate leaf reflectance measurements as a tool to identify and quantify disease severity and to discriminate between different diseases. Wheat plants were inoculated under controlled conditions in different intensities either with powdery mildew or take-all. Leaf reflectance was measured with a digital imager (Leica S1 Pro, Leica, Germany) under controlled light conditions in various wavelength ranges covering the visible and the near-infrared spectra (380–1300 nm). Leaf scans were evaluated by means of L*a*b*-color system. Visual estimates of disease severity were made for each of the epidemics daily from the onset of visible symptoms to maximum disease severity. Reflectance within the ranges of 490₇₈₀ nm (r² = 0.69), 510₇₈₀nm (r² = 0.74), 516₁₃₀₀nm (r² = 0.62) and 540₁₃₀₀ nm (r² = 0.60) exhibited the strongest relationship with infection levels of both powdery mildew and take-all disease. Among the evaluated spectra the range of 490₇₈₀nm showed most sensitive response to damage caused by powdery mildew and take-all infestation. The results of this study indicated that disease detection and discrimination by means of reflectance measurements may be realized by the use of specific wavelength ranges. Further studies have to be carried out, to discriminate powdery mildew and take-all infection from other plant stress factors in order to develop suitable decision support systems for site-specific fungicide application.     

Greenhouse screening ofTrichoderma isolates for control ofCurvularia leaf spot of yam

TenTrichoderma isolates were studied under greenhouse conditions as potential agents for biocontrol of yam leaf spot, caused byCurvularia eragrostidis. TheTrichoderma isolates demonstrated high efficiency of disease control. Application of the antagonists on the same day asC. eragrostidis inoculation showed the best results. One isolate achieved 75 percent disease severity reduction. The survival of theTrichoderma isolates decreased after its application on the phylloplane with values of 57 and 41 percent at the 49th day, in the absence and presence of the phytopathogen respectively. The antagonism persisted well againstC. eragrostidis, the TN1 isolate praises 89 percent.     

Evaluation of elite genotypes of mungbean against Cercospora leaf spot disease (CLS) caused by Cercospora canescens

The AUDPC is the best measurement of CLS disease of mungbean, since it is based on several readings of disease intensity from the early to the mature stage. Thirty-one genotypes of the mungbean crop showed similar disease reactions at later stages both under the polyhouse and field conditions. Under field conditions, 22 genotypes were found moderately resistant, seven susceptible and two genotypes were highly susceptible, and under polyhouse conditions eight genotypes showed resistance, 19 moderate resistance and four genotypes were found susceptible.     

Induction of resistance against Cercospora leaf spot in safflower by seed treatment with plant growth-promoting rhizobacteria

Out of seven isolates of rhizobacteria, four strains including GBO-3, INR937a, INR937b and IPC-11 were selected as inducers of systemic resistance against Cercospora carthami and tested individually for biological control of different important seed-borne fungal pathogens. The level of control achieved by each rhizobacterium varied with the pathosystem studied. The isolates GBO-3, INR937a, INR937b and IPC-11 exhibited reduced disease intensity in terms of average number of leaf lesions as compared to untreated control in protection experiments against C. carthami. Micromobilised with rhizobacterium GBO-3, INR937a, INR937b and IPC-11 safflower seeds were grown under greenhouse and challenge inoculated with C. carthami were selected for estimation of lipoxygenase, polyphenylalanine ammonia-lyase, peroxidase, polyphenol oxidase and β-1,3 glucanase activities were estimated spectrophotometrically. Increase in all enzymes was detected in foliar extracts from plants at different stages after challenge inoculation.     

De novo indol-3-ylmethyl glucosinolate biosynthesis,and not long-distance transport,contributes to defence of Arabidopsis against powdery mildew

Powdery mildew is a fungal disease that affects a wide range of plants and reduces crop yield worldwide. As obligate biotrophs, powdery mildew fungi manipulate living host cells to suppress defence responses and to obtain nutrients. Members of the plant order Brassicales produce indole glucosinolates that effectively protect them from attack by non-adapted fungi. Indol-3-ylmethyl glucosinolate is constitutively produced in the phloem and transported to epidermal cells for storage. Upon attack, indol-3-ylmethyl glucosinolate is activated by CYP81F2 to provide broad-spectrum defence against fungi. How de novo biosynthesis and transport contribute to defence of powdery mildew-attacked epidermal cells is unknown. Bioassays and glucosinolate analysis demonstrate that GTR glucosinolate transporters are not involved in antifungal defence. Using quantitative live-cell imaging of fluorophore-tagged markers, we show that accumulation of the glucosinolate biosynthetic enzymes CYP83B1 and SUR1 is induced in epidermal cells attacked by the non-adapted barley powdery mildew Blumeria graminis f.sp. hordei. By contrast, glucosinolate biosynthesis is attenuated during interaction with the virulent powdery mildew Golovinomyces orontii. Interestingly, SUR1 induction is delayed during the Golovinomyces orontii interaction. We conclude that epidermal de novo synthesis of indol-3-ylmethyl glucosinolate contributes to CYP81F2-mediated broad-spectrum antifungal resistance and that adapted powdery mildews may target this process.