Inheritance of the resistant reaction of the lettuce cultivar `Grand Rapids' to the southern root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood

Resistance to the southern root-knot nematode Meloidogyne incognita Chitwood would be an important attribute of lettuce Lactuca sativa L. cultivars adapted to both protected and field cultivation in tropical regions. `Grand Rapids' and a few other cultivars are reported to be resistant to this nematode. In this paper, we studied the inheritance of the resistant reaction of `Grand Rapids' (P₂) in a cross with a standard nematode-susceptible cultivar Regma-71 (P₁). F₁(Regina-71 × Grand Rapids) and F₂ seed were obtained, and inoculated along with the parental cultivars with different races of M. incognita to evaluate nematode resistance. Broad sense heritability estimates for the number of galls and of egg masses per root system, gall size and gall index were generally in the order of 0.5 or higher. Class distributions of these variables over generations P₁, P₂, F₁ and F₂ were in agreement with simulated theoretical distributions based on monogenic inheritance models. F₃ families were obtained from randomly sampled F₂ plants and tested for reaction to the nematode. The frequency ratio of homozygous resistant, segregating and homozygous susceptible F₃ families did not differ from the 1:2:1 ratio expected from monogenic inheritance. M. incognita resistance appears to be under control of a single gene locus. The Grand Rapids allele (for which the symbol Me is proposed) is responsible for the resistant reaction, and shows high (though incomplete) penetrance, variable expressivity and predominantly additive gene action. This revised version was published online in July 2006 with corrections to the Cover Date.     

广东省稻瘟病菌生理小种的消长动态

１９９０～１９９７年,用中国稻瘟病菌鉴别寄主鉴定了广东省稻瘟病菌单孢菌株１５７４份,共鉴定出８群４３个生理小种。其中ＺＣ群一直是广东省的优势种群,其出现频率平均为５０.２％;ＺＣ_１３一直是优势小种,其出现频率平均为２７.４％,其次是ＺＧ_１（１８.８％）、ＺＣ_１５（１４.５％）和ＺＢ_１３（９.１％）小种。不同地区不同年份优势小种的类型及其组成不同。     

Characterization of two races of the stem and bulb nematode (Ditylenchus dipsaci) in Israel

Two distinct races ofDitylenchus dipsaci in Israel were identified: one, which infects and damages onion and garlic, reproduces on pea, but does not infect phalaris grass; and a second, which infects and damages phalaris—and, probably, also ‘Saia’ oats—but fails to infect onion and garlic. A new ‘garlic’ race of the nematode does not appear to have been introduced into Israel together with the ‘Lavinia’ garlic cultivar, as previously speculated, but rather the introduced Lavinia clone is highly susceptible to the existing ‘onion and garlic’ race ofD. dipsaci.     

A study on the pathogen species and physiological races of tomato Fusarium wilt in Shanxi,China

In order to clarify the main pathogens of tomato Fusarium wilt in Shanxi Province, China, morphological identification, elongation factor 1 alpha(EF-1α) sequence analysis, specific primer amplification and pathogenicity tests were applied to study the isolates which were recovered from diseased plants collected from 17 different districts of Shanxi Province. The results were as follows: 1) Through morphological and molecular identification, the following 7 species of Fusarium were identified: F. oxysporum, F. solani, F. verticillioides, F. subglutinans, F. chlamydosporum, F. sporotrichioides, and F. semitectum; 2) 56 isolates of F. oxysporum were identified using specific primer amplification, among which, 29, 5 and 6 isolates were respectively identified as F. oxysporum f. sp. lycopersici physiological race 1, race 2, and race 3; 3) pathogenicity test indicated the significant pathogenicity of F. oxysporum, F. solani, F. verticillioides, and F. subglutinans to tomato plant. Therefore, among these 4 species confirmed as pathogenic to tomato in Shanxi, the highest isolation rate(53.3%) corresponded to F. oxysporum. Three physiological species, race 1, race 2, and race 3 of F. oxysporum f. sp. lycopersici are detected in Shanxi, among which race 1 is the most widespread pathogen and is also considered as the predominant race.     

In vitro growth of Gremmeniella abietina isolates (European race) at different temperatures

The mycelial growth of 24 isolates of types A and B of Gremmeniella abietina (Lagerb.) Morelet, collected in northern Finland and the Kola peninsula, Russia, was studied on malt agar plus pine needle extract at 18°C and 5°C. Great variation occurred within both types, and the results suggest that several isolates per stand are needed to represent one local isolate, if responses of G. abietina mycelia are studied on artificial media.     

Durability of resistance in lily to basal rot: evaluation of virulence and aggressiveness among isolates ofFusarium oxysporum f. sp.lilii

Prospects of durability of resistance in lily to basal rot have been evaluated by testing the virulence and aggressiveness of 31 isolates ofFusarium oxysporum f. sp.lilii towards a number of different resistance sources inLilium spp. Isolates differed strongly in aggressiveness as did species and cultivars ofLilium spp. in resistance. Significant interactions were observed between isolates of the pathogen and genotypes ofLilium spp., but the magnitude was very small compared to the main effects. The interactions were mainly due to a small group of isolates with low aggressiveness. It is argued that the interactions might be based on minor genes. No major break down of the resistance was found. For practical purposes it will be sufficient to use highly aggressive isolates in screening tests.     

Production of Beauvericin by Different Races of Fusarium Oxysporum F. sp. Melonis, The Fusarium Wilt Agent of Muskmelon

Fourty-four strains of Fusarium oxysporum were isolated from plants of melon with Fusarium wilt symptoms. Among these strains, thirty-nine were characterized for their pathogenicity on melon. Thirty-seven strains belonged to known races of F. oxysporum f. sp. melonis, while two strains were non-pathogenic. Four strains belonged to race 0, seven to race 1, four to race 2, and twenty-two to race 1,2. Beauvericin was produced by thirty-six strains in a range from 1 to 310gg^–1. Eight isolates of race 1,2 did not produce the toxin. In addition, of the two non-pathogenic strains, only one strain produced the toxin (290gg^–1). The production of enniatin A₁, enniatin B₁, and enniatin B was also investigated. Enniatin B was the only enniatin detected, being produced by eleven strains belonging to all the races, with a range of production from traces to 60gg^–1. Finally, melon fruits belonging to two different cultivars (Cantalupo and Amarillo) were artificially inoculated with one strain of F. oxysporum f. sp. melonis (ITEM 3464). Beauvericin was detected in the fruit tissues of both cultivars at a level of 11.2 and 73.8gg^–1, respectively. These data suggest that the production of both the toxins is not related to the pathogenicity of F. oxysporum f. sp. melonis, nor to the differential specificity of the races. The results confirm that beauvericin is a common metabolite of phytopathogenic Fusarium species.     

Breakdown of Pl2, a major gene of resistance to apple powdery mildew, in a French experimental orchard

Pl2 , a major resistance gene to powdery mildew originating from Malus zumi , is mainly used in apple-breeding programmes. In an experimental orchard in France, an increase of susceptibility to powdery mildew was observed on apple genotypes carrying Pl2 . This increase of susceptibility could not be explained by an effect of the age of the trees, or by an effect of the amount of inoculum on expression of the resistance Pl2 . It was demonstrated by tests of pathogenicity in controlled conditions that isolates of Podosphaera leucotricha sampled in this orchard were virulent to Pl2 . The appearance of virulent isolates within 6 years after planting apple genotypes selected for the presence of Pl2 resulted in a breakdown of the resistance. Ten years after planting, the percentage of genotypes that were still resistant to powdery mildew varied between 2 and 56%, depending on the progenies. This suggested that additional quantitative resistance genes may influence the durability of the resistance Pl2 .     

Patterns of genetic diversity in landraces of common bean (Phaseolus vulgaris L.) from Galicia

Knowledge of patterns of genetic diversity among existing cultivars helps to broaden the genetic base of new cultivars and maximizes the use of available germplasm resources. This study examined the organization of diversity for morphological traits in 66 landraces of cultivated common bean (Phaseolus vulgaris) from Galicia and its relationship with phaseolin seed protein diversity. Data on growth habit, seed and pod traits obtained from field evaluations at two locations during the 1989—91 cropping seasons were subjected to multivariate statistical analysis. Cluster analysis based on 14 quantitative variables and five qualitative variables identified 11 groups. The landraces were also characterized by phaseolin electrophoresis. The results allowed separation of these landraces into Middle and Andean American groups, which could be further divided into at least eight groups within the Andean American cultivars and three within the Mesoamerican cultivars. These groups in turn corresponded to the previously described races Nueva Granada and Peru of South American origin, and races Durango, Jalisco and Mesoamerica from the Middle American domestication centre. These results confirm the existence of two major groups of germplasm in the cultivated common bean landraces from Galicia, Mesoamerican vs. Andean American.     

云南咖啡抗锈品种抗锈性丧失原因及防治对策

针对云南咖啡抗锈品种不同植区出现锈病,结合国内锈病小种分布情况,开展了咖啡大田抗锈性丧失原因的调查研究,结果表明:寄主-病原菌-环境的相互作用,使咖啡锈病生理小种不断变异,导致抗锈性丧失,阐述了持久抗锈品种选育研究和合理配置对咖啡品种抗锈持久的重要性,提出了防治锈病的措施。