Genetic diversity of Soybean Cyst Nematode (Heterodera glycines) populations in Southeastern Goiás state, Brasil

Heterodera glycines, also known as Soybean Cyst Nematode (SCN), is one of the phytosanitary issues that prevents high soybean yields (Glycine max) due to its dissemination capacity and high physiological race variability. The first step towards the proper and safe use of resistant cultivars lies on correctly identifying the physiological race of this nematode in the crop in order to avoid new breed-selection pressure. Thus, the aim of the present study was to genetically characterize the races of Heterodera glycines populations from soybean-producer counties belonging to the Railroad (Estrada de Ferro) Region (Goiás State, Brazil), as well as to investigate their molecular characterization based on RAPD markers. RAPD data were evaluated in a binary way, in which values (1) and (0) were attributed to the presence and absence of amplified bands for each primer, respectively. The binary matrix was used to estimate the genetic distance between populations, based on the Jaccard dissimilarity index. The clustering analysis was carried out based on the calculated genetic dissimilarity matrix, according to Ward’s method. Eight (8) different physiological Heterodera glycines races were found in the investigated counties. Only 10 out of 28 RAPD primers were polymorphic among SCN populations, whereas the remaining primers either did not amplify, or presented low amplification of the DNA fragment. Five genetically-different groups were recorded among H. glycines population accessions, which presented high genetic variability rate.

Genetically Diverse Long-Lived Clonal Lineages of Phytophthora capsici from Pepper in Gansu, China

Phytophthora capsici causes significant loss to pepper production in China, and our objective was to investigate the population structure in Gansu province. Between 2007 and 2011, 279 isolates were collected from pepper at 24 locations. Isolates (or subsets) were assessed for simple sequence repeat (SSR) genotype, metalaxyl resistance, mating type, and physiological race using cultivars from the World Vegetable Center (AVRDC) and New Mexico recombinant inbred lines (NMRILs). The A1 and A2 mating types were recovered from nine locations and metalaxyl-resistant isolates from three locations. A total of 104 isolates tested on the AVRDC panel resolved five physiological races. None of 42 isolates tested on the NMRIL panel caused visible infection. SSR genotyping of 127 isolates revealed 59 unique genotypes, with 42 present as singletons and 17 having 2 to 13 isolates. Isolates with identical genotypes were recovered from multiple sites across multiple years and, in many cases, had different race types or metalaxyl sensitivities. Isolates clustered into three groups with each group having almost exclusively the A1 or A2 mating type. Overall it appears long-lived genetically diverse clonal lineages are dispersed across Gansu, outcrossing is rare, and functionally important variation exists within a clonal framework.

Identification of Novel Physiological Races of Phytophthora capsici Causing Foliar Blight Using the New Mexico Recombinant Inbred Pepper Lines Set as a Host Differential

Phytophthora foliar blight caused by Phytophthora capsici is a serious limitation to pepper (Capsicum annuum) production worldwide. Knowledge of the physiological race composition of isolates causing phytophthora foliar blight is necessary for success in breeding for disease resistance. The New Mexico recombinant inbred lines (NMRILs) effectively differentiated isolates from different geographical locations (i.e., Turkey, The Netherlands, Argentina, and two states in the United States) into 12 physiological races of P. capsici causing phytophthora foliar blight. This research demonstrates the use of the NMRILs to identify P. capsici foliar blight races and the importance of identifying the physiological races occurring in specific regions where a C. annuum cultivar will be grown. Knowing the physiological race(s) in a region will provide valuable information to formulate breeding strategies to deploy durable foliar blight resistance.

Lima Bean Downy Mildew Epiphytotics Caused by New Physiological Races of Phytophthora phaseoli

Before 1995, race D of Phytophthora phaseoli, the causal agent of downy mildew on lima bean (Phaseolus lunatus), was the prevalent physiological race in the mid-Atlantic region of the United States. Since 1995, however, new physiological races of P. phaseoli have been responsible for downy mildew outbreaks in previously resistant cultivars in this region. Cultivar differential testing of 180 isolates of P. phaseoli collected between 1994 and 2005 from Delaware and the eastern shore of Maryland has confirmed the presence of two new physiological races. The detection of race E in 1995 and race F only 5 years later in 2000, plus the lack of resistant cultivars to manage the epiphytotics in lima bean, have led to millions of dollars of crop losses. Intra- and interspecific genetic variation of Phytophthora spp. and isolates were assessed using amplified fragment length polymorphism DNA fingerprinting. Primer groups EcoRI+AG and MseI+C distinguished P. phaseoli and P. capsici from P. infestans but did not distinguish among different races of P. phaseoli.

Identification of Physiological Race Nematode, Radopholus similisCobb. that Attack Coffee Trees

Physiological races of Radopholus similis Cobb., the burrowing nematode that attack coffee trees have never been reported yet, while two physiological races have been identified, i.e. banana and citrus races. Banana and citrus are commonly used as the shading trees or crop diversification in coffee plantation. Therefore, both races have to be analyzed whether the same as the race that attacking the coffee plants. Research to investigate the physiological race of R. similis Cobb. had been conducted in the screen house at Indonesian Coffee and Cocoa Research Institute, Jember. The experiment was arranged in randomized complete design with three replications, while cross inoculation tests were used as race identification method, by using three isolates from banana, citrus and Arabica coffee as the control. Tested host plants were banana Cavendish, ‘Ambon Kuning’ and ‘Raja’ varieties, rootstock of citrus Siam from Kintamani and Arabica coffee Kartika 1 variety. The expression of virulence of three nematode isolates against banana, citrus or arabica coffee tested to be considered as favorable host, while the most virulent isolate attacked coffee could be decided as physiological race of coffee. Results showed that banana isolate penetrated and attacked the roos of arabica coffee. The isolate of R. similis from citrus could not attack both coffee and banana varieties. Therefore, the physiological race of coffee was considered similar with the banana race. It was possible that the physiological race was specific race but it could attacke banana as other favorable host, however, it could not be proven in this results. Based on this results, the use of Musa sp.as intercrop or shade tree in coffee plantation has more risk to nematode attack than that of Citrus sp. Key words: physiological race, Radopholus similis, coffee, banana, citrus, nematode.