In vivo control of Mycosphaerella pinodes on pea leaves by a crude bulb extract of Eucomis autumnalis

We previously reported on the in vitro antifungal activity of a crude whole plant extract from Eucomis autumnalis against seven economically important plant pathogenic fungi. A crude extract of the bulb showed similar in vitro mycelial growth inhibition of the same plant pathogenic fungi as well as that of an eighth fungus, Mycosphaerella pinodes, the cause of black spot or Ascochyta blight, in peas. Subsequently, fourth internode leaves were removed from 4 wk old pea plants, placed on moist filter paper in Petri dishes and inoculated with an M. pinodes spore suspension before and after treatment with the extract. The control of Ascochyta blight by different concentrations of the crude E. autumnalis extract was followed in vivo by leaf symptoms over a 6 day period at 20°C in a growth cabinet. The crude extract prevented M. pinodes spore infection of the leaves when the leaves were inoculated with spores both before or after treatment with the extract, confirming complete inhibition of spore germination. The crude E. autumnalis extract showed no phytotoxic reaction on the leaves even at the highest concentration applied.     

Improving chickpea yield by incorporating resistance to ascochyta blight

Ascochyta blight [Ascochyta rabiei (Pass.) Lab.] is the most destructive disease of chickpea (Cicer arietinum L.), but it can be managed effectively by the use of resistant cultivars. Therefore, a breeding programme was initiated during 1977–78 at ICARDA, Syria, to breed blight-resistant, high-yielding chickpeas with other desirable agronomic traits. Crosses were made in main season at Tel Hadya, Syria, and the F₁s were grown in the off season at Terbol, Lebanon. The F₂, F₄ and F₅ generations were grown in a blight nursery in the main season where blight epidemic was artificially created. The plants and progenies were scored for blight resistance and other traits. The F₃ and F₆ generations were grown in the off season under normal day length to eliminate late-maturing plants. The pedigree method of breeding was followed initially, but was later replaced by the F₄-derived family method. The yield assessment began with F₇ lines, first at ICARDA sites and later internationally. A total of 1584 ascochyta blight-resistant chickpea lines were developed with a range of maturity, plant height, and seed size not previously available to growers in the blight-endemic areas in the Mediterranean region. These included 92 lines resistant to six races of the ascochyta pathogen, and 15 large-seeded and 28 early maturity lines. New cultivars produced 33% more seed yield than the original resistant sources. The yield of chickpea declined by 340 kg ha^-1, with an increase in blight severity by one class on a 1–9 scale, reaching zero yield with the 8 and 9 classes. Development of blight-resistant lines made the introduction of winter sowing possible in the Mediterranean region with the prospect of doubling chickpea production. Twenty three cultivars have been released so far in 11 countries.Joint contribution from ICARDA and ICRISAT. ICRISAT Journal Article no. JA 1886.     

鹰嘴豆种质资源对Ascochyta rabiei的抗性评价及遗传多态性分析

以25 个鹰嘴豆品系为试验材料,通过叶面喷雾的方式进行Ascochyta rabiei菌悬液室内外人工接种,评价不同鹰嘴豆种质资源的抗病性;同时利用RAPD方法进行基因型鉴定,采用NTSYSpc 2.10t软件对分子标记结果进行遗传相似性的统计分析并建立各品系间的亲缘关系聚类图,探讨不同鹰嘴豆品系对A.rabiei抗性与遗传多态性间的关系。通过室内和田间鹰嘴豆抗A.rabiei鉴定结果综合分析表明：在25个鹰嘴豆供试品系中,“系选 03”和“216”品系均表现出稳定抗性特性;北园春品系表现出稳定中抗特性。通过RAPD多态性引物对这25 个供试品系进行PCR扩增,共获得129 个扩增条带,其中多态性条带共有67 条,多态性比例达51.94%,遗传相似系数为0.3731-0.9254。结合抗病性和遗传多态性,经方差分析表明,本研究所采用的鹰嘴豆品系对A.rabiei的抗性强弱与其遗传相似性之间无显著相关性。     

The talc formulation of Streptomyces antagonist against Mycosphaerella foot rot in pea (Pisum sativum l.) seedlings

Pea is highly susceptible to pre-emergence damping off and foot rot after emergence caused by Mycosphaerella pinodes in western Algerian regions. Rhizosphere Actinomycetes which were antagonistic to the growth of this pathogen were isolated from chellif soils. An isolate of Streptomyces St7c5 provided superior seed protection. An increased in both germination and plant growth were recorded following treatment of seeds with Streptomyces formulated with inert or organic charge when compared to control. Application of the antagonist agent resulted in a significant reduction of Mycosphaerella foot rot to 5% compared with untreated seeds (25%). Hence, the talc formulation of Streptomyces agent can be recommended as one of the crop strategies for the management of foot rotting and blight caused by Mycosphaerella pinodes.     

Distribution of Mating Types and Genetic Diversity of Ascochyta rabiei Populations in Tunisia Revealed by Mating-type-specific PCR and Random Amplified Polymorphic DNA Markers

The distribution of mating types of Ascochyta rabiei (teleomorph: Didymella rabiei) was determined in Tunisia using a MAT‐specific PCR assay. Among 123 isolates tested, 80% were MAT1‐1 and 20%MAT1‐2. Only MAT1‐1 isolates were present in the Beja and Bizerte regions of Tunisia, whereas both mating types were present in Nabeul, Kef and Jendouba. In the latter three regions, the hypothesis of random mating could not be rejected based on chi‐squared tests of mating‐type ratios (P > 0.05). The lower frequency of the MAT1‐2 coupled with the restricted distribution of this mating type in Tunisia may indicate a recent introduction of MAT1‐2 in Tunisia. This speculation is consistent with the recent (2001) observation of D. rabiei pseudothecia on chickpea debris in Tunisia. Forty isolates representative of the five regions were genetically analysed using 10 random amplified polymorphic DNA (RAPD) primers to provide a preliminary estimate of genetic diversity of the pathogen in Tunisia. Among 129 putative RAPD loci amplified, 81% were polymorphic and 32 unique RAPD fingerprints were detected. A high level of genetic differentiation was detected among subpopulations (G_ST = 0.33). Cluster analyses revealed that isolates from Bizerte, Beja and Jendouba were genetically similar and distinct from isolates sampled in Nabeul and Kef. MAT1‐1 isolates were clustered separately from MAT1‐2 isolates in Jendouba and Nabeul suggesting that recombination may not yet be occurring in these regions despite the occurrence of both mating types in equal frequency in these regions. This lack of recombination between MAT1‐1 and MAT1‐2 also supports the hypothesis of a recent introduction of MAT1‐2 into Tunisia.     

Histological and Ultrastructural Changes in Leaves and Stems of Resistant and Susceptible Chickpea Cultivars to Ascochyta rabiei

The histo- and cytopathological effects in resistant (ILC-195) and susceptible (Canitez-87) chickpea cultivars were examined by light, transmission and scanning electron microscopy 3, 5 and 7 days after inoculation (d.a.i) of seedlings with Ascochyta rabiei. The fungus produced typical appressoria that penetrated both cuticle and stomata. The resistant plants had physical barriers and a cuticle layer against fungal penetration 3 d.a.i. The fungus spread intercellularly and subepidermally in the leaves and stems of susceptible plants 3 d.a.i., and was followed 5 d.a.i. by cell plasmolysis, degeneration of organelles and of cellulose, but not lignified, walls. Pycnidia formation occurred between 5 and 7 d.a.i. 7 d.a.i., organelle degeneration, pycnidia formation and symptom severity increased. Tracheidal elements, including lignified elements, were almost intact in both resistant and susceptible cultivars. In the susceptible plants, lignin cell walls were slightly degraded after 7 days. There was less cell degeneration and pycnidia formation in resistant plants. Some electron-dense large bodies and lipid granules were observed within intracellular fungal hyphae in infected cells of resistant plants 7 d.a.i.     

Host Specificity and Genetic Diversity of Didymella bryoniae from Cucurbitaceae in Brazil

Thirty‐seven isolates of Didymella bryoniae from three Cucurbitaceae species were collected in Brazil and tested for pathogenicity to watermelon. All isolates were pathogenic but differed in aggressiveness levels. Seven representative isolates were used in cross‐pathogenicity tests against 10 cucurbitaceous hosts. Most isolates were pathogenic to most host species tested, except to Sechium edule. Among the susceptible species, Citrullus and Cucumis species were the most susceptible hosts, while pumpkin and Luffa purgans were the most resistant. Host of origin affected the pattern of aggressiveness on each host. Isolates from watermelon were very aggressive to their original host, but much less aggressive or not pathogenic at all to some Cucurbita. Two previously described random‐amplified polymorphic DNA (RAPD)‐specific primers indicated that 81% of the isolates could be classified into the so‐called RG I group, while the remaining isolates could not be classified into any of the described RG groups. All 37 isolates were further characterized by RAPD fingerprinting and compared with three US isolates representative of RG I and RG II groups. The Brazilian D. bryoniae isolates could be separated into genetically similar clusters. The majority of the isolates were grouped in cluster DB Ia, which contained only isolates of Citrullus lanatus and Cucumis melo. Two of the American isolates used as controls clustered with this group at 68% similarity level. The DB Ib cluster included three Brazilian isolates obtained from melon and watermelon and the American representative for RG II, at a lower similarity level (43%). Two isolates from watermelon clustered with one isolate from melon in a separate group (DB II), while one single isolate from pumpkin (DB III) showed the lowest genetic similarity to all other isolates. Didymella bryoniae isolates from Brazil showed, therefore, a level of genetic diversity higher than previously reported for the species. RAPD fingerprinting allowed for geographical distinction of D. bryoniae isolates but no correlation between genetic distance, aggressiveness or origin of the isolate was found.     

球壳孢目真菌个体发育研究Ⅰ:壳二胞等四属

人工培养条件下,用光学显微镜和透射电子显微镜对球壳孢目（Sphaerosidales）的Ascochyta,Phyllosticta,Phomopsis,Septoria四属进行个体发育研究,明确了其产孢方式：Ascochyta和Phyllosticta为内壁芽生瓶梗式;Phomopsis为全壁芽生瓶梗式;Septoria为全壁芽生合轴式,这一结果为属级分类提供了可靠的依据。产孢方式是属内共同具有的稳定特征,分生孢子的形成方式类型、产孢细胞及分生孢子的形态是划分属的首要标准。以寄主植物属为基础确定的同属大多数种在个体发育上无明显差别,分生孢子的形态及大小是分种的一个重要依据。