Effects of an arbuscular mycorrhizal fungus and two plant-parasitic nematodes on<Emphasis Type="Italic"> Musa</Emphasis> genotypes differing in root morphology

In this study, the effect of an arbuscular mycorrhizal fungus (AMF) and two migratory endoparasitic nematodes on Musa plant growth, including the root system, were examined. In addition, the AMF-nematode interaction was studied. Seven Musa genotypes with different root systems were selected. Based on their relative mycorrhizal dependency, two genotypes (Calcutta 4 and Obino l'Ewai) were selected for AMF-nematode interaction studies. The experiments were performed under greenhouse conditions. Mycorrhization with Glomus mosseae resulted in a significantly better plant growth even in the presence of nematodes. The effect of AMF on the root system was genotype-dependent and seemed to be related to the relative mycorrhizal dependency of the genotype. The nematodes also affected the root system, decreasing branching. Nematode population densities were significantly reduced in the presence of AMF, except for Pratylenchus coffeae in Obino l'Ewai. In the root system, it appeared that the decreased branching caused by the nematodes was counterbalanced by the increased branching caused by the AMF.     

培养时间和接种密度对咖啡短体线虫繁殖和形态的影响

采用胡萝卜片培养短体线虫技术,测试不同培养时间和接种密度对咖啡短体线虫(Pratylenchus coffeae)繁殖和形态的影响。结果表明,在25℃培养条件下,每片胡萝卜(厚10 mm,直径3 cm)接种25头线虫雌虫,线虫的数量随培养时间的延长而增加,前3周线虫的繁殖系数为6.24,线虫的群体数量增长缓慢;第3~6周线虫的繁殖系数略有增高,为8.99;第6~9周其繁殖系数高达17.88,线虫群体数量快速增长;之后,线虫群体数量增速下降,其繁殖系数降为1.42。在接种不同密度线虫的实验中,线虫的群体数量均显著增长,其繁殖系数在不同接种密度处理中差异不显著;随机挑取10头雄虫与雌虫,比较不同线虫密度对线虫形态特征的影响,结果表明,线虫密度除对雌虫的b值(体长/头顶至食道腺与肠连接处长)有显著影响外,对雄虫和雌虫的其他形态特征测量值均无显著影响。     

Detection and analysis of inter- and intraspecific diversity of Pratylenchus spp. using isozyme markers

The root-lesion nematodes of the genus Pratylenchus are an economically important group of plant parasitic nematodes that show high similarity among sibling species. Isozyme patterns obtained by isoelectrofocusing (IEF) were used to differentiate and establish genetic relatedness among Pratylenchus species. A total of 40 populations comprising 9 Pratylenchus species and Radopholus similis from broad host and geographic origins was examined to compare isozyme patterns of esterase (EST), hexoquinase (HK), isocitrate dehydrogenase (IDH), malate dehydrogenase (MDH), phosphoglucose isomerase (PGI), phosphoglucomutase (PGM) and superoxide dismutase (SOD). Of these systems, only EST, MDH, PGI and PGM were useful for differentiation of P. vulnus , P. goodeyi , P. penetrans , P. scribneri , P. thornei and R. similis populations. The greatest intraspecific diversity was found within P. coffeae based on the isozyme patterns for MDH, PGI and PGM. Intraspecific variability was also detected among R. similis populations, which showed two isozyme patterns in EST and PGI systems. Less intraspecific variation was found within the P. penetrans group. The P. goodeyi population from Cameroon differed from the other populations in this specific group in its MDH, PGI and PGM phenotypes. Highly similar banding patterns of EST, MDH and PGI activity were found among the P. scribneri populations and the one population of P. agilis . A cluster analysis of the 40 populations, generated from the four enzyme banding patterns, produced groupings that broadly matched the previous classification into specific groups, reflecting intraspecific variability in some cases. The results confirm the potential use of isozyme patterns as markers for these nematode species and their value for diagnostic application.     

Nematode resistance in bananas: screening results on some wild and cultivated accessions of Musa spp.

Bananas cultivated for export all belong to Cavendish cultivars and are all recognized as very susceptible to nematodes, particularly to the burrowing nematode Radopholus similis and the lesion nematode Pratylenchus coffeae. Even if there have been many changes in the management of banana nematodes in large commercial banana plantations, chemical control still remains most often the last resort method to manage the nematodes, although the number of registered products is definitely declining. Therefore, nematode control though genetic improvement is gaining new interest worldwide. In this study, 55 banana accessions mostly diploids from the Musa acuminata genome group (AA) but including some triploid accessions (AAA), some diploids of the Musa balbisiana genome group (BB) and some interspecific hybrids (AAB, AB) were evaluated for resistance to four nematode species R. similis, P. coffeae, Meloidogyne incognita and M. arenaria. These experiments were conducted in a growth chamber under controlled conditions. All banana accessions were susceptible to nematode species, although many different levels of susceptibility were detected. This study confirmed the good resistance status to R. similis of some cultivars from the Pisang jari buaya and Pisang batuau subgroups and the partial resistance of 17 diploid accessions significantly different from the susceptible reference cv. Grande Naine. This study also showed that 12 diploid accessions exhibited a partial resistance to P. coffeae, including some usual or potential genitors belonging to the wild diploids subspecies burmannica (cvs. Long Tavoy 1 and 2) and burmannicoides (cv. Calcutta 4). No source of resistance to Meloidogyne spp. was found. These screening results, combining for the first time four nematode species, are discussed within the scope of banana breeding in order to produce parental diploid lines with single or combined nematode resistances and further develop triploids that can substitute existing susceptible commercial cultivars.     

Relationships between soil penetration resistance and soif nematode burden in barley on Prince Edward Island

Fifty sloping fields of barley with different short-term cropping histories across Prince Edward Island were examined for variations in root-zone depth and the severity of soil parasitic nematodes as part of a wider study of relationships between cropping sequence, topographic position, soil physical conditions and crop performance. Root lesion nematode (Pratylenchus penetrans) density in the roots was significantly greater (13%) at foot slopes than at top slopes, and stunt nematode (Tylenchorhynchus spp.) was significantly greater (8%) at top slopes where the soil was drier. The density of stunt nematodes and root lesion nematodes in the soil was significantly greater (>15%) under miscellaneous cereals-barley sequences than under potato-barley or hay-barley, attributable to level of carryover. Root lesion nematode density in the roots was significantly greater (12%) under hay-barley than either of the other two sequences. This nematode also showed a strong tendency to increase in number with increasing root-zone depth, and may be explained on the basis that increased root-zone depth provides increased host root mass (substrate). Stunt nematodes, on the other hand, increased with decreasing root-zone depth and may be explained by the known propensity of these organisms for drier, shallower soil conditions.     

云南花卉短体线虫记述*

 根据形态特征和测量数据从云南26种花卉标本中,初步鉴定出3种短体线虫:伤残短体线虫(Pratylenchus vulnus)、咖啡短体线虫(P. coffee)、穿刺短体线虫(P. penetrans),它们均为云南省首次报道。     

Global status of nematode problems of groundnut, pigeonpea, chickpea, sorghum and pearl millet, and suggestions for future work

Analysis of responses received from 40 cooperators in 20 countries to a questionnaire on nematode problems of groundnut, pigeonpea, chickpea, sorghum and pearl millet suggested that Meloidogyne spp. are internationally important nematode pests of groundnut, chickpea and pigeonpea. Pratylenchus spp. are important on all the five crops. In India, Heterodera cajani and Rotylenchulus reniformis are important pathogens of pigeonpea. Over the last 10–15 years, extensive nematode disease surveys have been undertaken for these crops in Australia, Egypt, India, Jamaica, Senegal, Sudan, Thailand and Zimbabwe; however, < 10% of the total crop areas were covered by these surveys. Except for Brazil, Egypt, USA and Zimbabwe, growers do not use nematicides to control the nematodes. Cultural practices, especially crop rotations, are the most commonly used control measures. Species of Meloidogyne, Pratylenchus and Rotylenchulus on the legumes, and species of Hoplolaimus, Pratylenchus, Quinisulcius and Xiphinema on the cereals, are strongly suspected of increasing the severity of fungal diseases. Work aimed at finding host resistance is being done in Brazil, Fiji, India and the USA, and some sources of resistance have been identified against Meloidogyne arenaria, M. incognita, M. javanica and R. reniformis. Facilities for resistance screening work now exist in many countries. Information on damage thresholds of important pest species are available only from Brazil, Fiji, India and the USA.     

云南水稻根际土壤中的线虫种类鉴定

描述了云南水稻根际土壤中发现的3种植物寄生线虫燕麦真滑刃线虫A phelenchus avenae Bastian, 1865,多带螺旋线虫Helicotylechus multicinctus (Cobb, 1893) Golden, 1956和穿刺短体线虫Pratylenchus penetrans (Cobb, 1917) Chitwood & Otifa, 1952.这3种寄生线虫均为云南省新记录.     

圆果大赤螨对茶红蜘蛛的捕食作用

圆果大赤螨对茶红蜘蛛捕食作用的拟合方程符合Holling圆盘方程Ⅱ型,功能反应受到猎物虫态、温度和捕食者密度的影响.圆果大赤螨成螨显著地趋向于取食茶红蜘蛛的幼螨和若螨,日均最高捕食量分别达49.31和38.65头,对卵和成螨的选择性较差.在相同猎物密度条件下,温度为15-30℃时,捕食数量随着温度的升高而增加;温度为(35±1)℃时捕食数量随着温度的升高而减少.温度为(30±1)℃时,捕食数量最大,这一温度与茶红蜘蛛秋季高峰期的温度相吻合.圆果大赤螨在捕食时存在种内干扰反应,随着捕食者密度的增大,日均捕食量逐渐减少,捕食作用也相应减弱,干扰系数m为0.7589,搜索常数Q为0.9983,E=0.9983P-0.7589.     

Path analysis: a novel approach to determine the contribution of nematode damage to East African Highland banana (Musa spp., AAA) yield loss under two crop management practices in Uganda

Damage caused by plant-parasitic nematodes on East Africa Highland banana cultivar Mbwazirume was evaluated at Sendusu, Central Uganda. Banana plots were either nematode-infested or non-infested and received either continuous heavy mulch or were finger millet (Eleusine coracana) inter-cropped. An infestation with banana weevil, Cosmopolites sordidus, occurred naturally. Suckers detached from third crop cycle harvested plants were indexed for root and corm damage. Nematodes were extracted from the indexed roots. Banana weevil damage was observed in a cross-section through the corm of the harvested plant. Relationships between root damage, corm damage and nematode population densities were examined using correlation analyses. Path analysis was used to establish their relative effects on bunch weight. Independent of the type of crop management, percentage root necrosis, percentage dead roots, Radopholus similis and Helicotylenchus multicinctus population densities were each negatively correlated with bunch weight. Banana weevil damage and Pratylenchus goodeyi population densities were not correlated with bunch weight (P≤0.05). Path analysis revealed that root necrosis under heavy mulching and dead roots under finger millet inter-crop were the major factors associated with reduced bunch weight. Independent of the type of crop management, path analysis demonstrated that R. similis and then H. multicinctus contributed most, and to a lesser extent P. goodeyi, to root necrosis and dead roots. C. sordidus damage to the inner or outer corm appeared not to affect bunch weight.