7th ICPP: new data on taxonomy, biology and control of several quarantine pests
At the 7th International Congress of Plant Pathology (Edinburgh, GB, 1998-08-09/16) several papers presented new data on taxonomy, biology and control of quarantine pests (or pests of quarantine interest), and the EPPO Secretariat has selected the following items. References only mention the names of the authors and the number of the abstract in the proceedings.
Small-spored Alternaria species. The taxonomy of small-spored Alternaria species and species groups is being revised based upon three-dimensional patterns of sporulation (observable at x50). RAPD analysis is also being used to evaluate the results obtained with morphological segregation. It is felt that these morphological characters can be used to differentiate small-spored Alternaria (A. alternata, A. gaisen, A. longipes,; A. infectoria, A. tenuissima and an arborescent group which has not yet been formally described). The authors stressed that the 'pathotype' system for naming small-spored Alternaria species should not be used (Serdani, M.; Crous, P.W.; Andersen, B.; Holz, G.; Mchau, G. - 2.2.5 ; Roberts, R.G.; Reymond, S.T. - 2.2.54).
Apple fruit crinkle viroid. Apple fruit crinkle viroid causes a graft-transmissible disease affecting apple fruit and bark. So far, this disease has only been recorded in Japan. The nucleotide sequence of apple fruit crinkle viroid has been studied, and preliminary comparisons have shown similarities with Australian grapevine viroid (which is only latent in grapevine) (Ito, T.; Sano, T.; Yoshida, K. - 3.7.6).
Bursaphelenchus xylophilus.
1) The genetic variability of Bursaphelenchus xylophilus (EPPO A1 quarantine pest) was studied in Japan, using RAPD. Intraspecific genetic variation exists among B. xylophilus isolated from Monochamus alternatus or from different stands of wilted Japanese black pine (Pinus thunbergii). In addition, B. xylophilus could be differentiated from B. mucronatus by using this technique (Akiba, M.; Kawabe, Y. - 3.7.78).
2) Control measures applied in Japan against pine wilt disease (caused by B. xylophilus) include: aerial spraying of insecticides against the vector Monochamus alternatus, insecticide treatments of timber already infested to prevent further spread, and trunk injection of chemicals active against the nematode. However, despite all these efforts, losses in pine timber have not decreased (Suzuki, K. - 3.7.6S).
3) Experiments have been made in Japan on the possible use of avirulent B. xylophilus to control pine wilt disease. Preliminary results showed that symptom development was delayed, although tree mortality was observed in the end (Kosaka, H.; Kiyohara, T.; Aikawa, T.; Ogura, N.; Tabata, K. - 3.7.68).
Ceratocystis fagacearum. The susceptibility of European oaks to Ceratocystis fagacearum (EPPO A1 quarantine pest) has been studied in USA. Results showed that European white oak species (Quercus robur, Q. petraea, Q. pubescens) could be seriously threatened by C. fagacearum if introduced into Europe, as significant mortality was observed (McDonald, W.L.; Tainter, F.H.; Pinon, J.; Double, M. - 4.6.3).
Cowpea golden mosaic and lima bean golden mosaic geminiviruses. Cowpea golden mosaic and lima bean golden mosaic geminiviruses are reported to infect respectively, Vigna spp. and lima beans (Phaseolus lunatus), in Nigeria. A golden mosaic disease is also found in wild relatives of cowpea, Vigna unguiculata subsp. dekindtiana (common perennial weed in Nigeria and West Africa). Molecular comparisons showed that the geminivirus infecting this weed is a strain of cowpea golden mosaic geminivirus, and that lima bean golden mosaic geminivirus is clearly a distinct virus. However, its possible relationships with viruses causing a similar disease in lima bean in South America remain to be studied (Thottappilly, G.; Winter, S.; Maxwell, D.P. - 1.11.7S).
Cryphonectria parasitica. Studies are being carried out on the potential use of dsRNA fungal viruses to control Dutch elm disease (Ophiostoma novo-ulmi) and Cryphonectria parasitica (EPPO A2 quarantine pest) (Brasier, C.M.; Milgroom, M.G. - 4.4.6S).
Leptographium genus. The anamorph genus Leptographium has been re-evaluated and an identification key proposed. The authors have also compiled a complete list of host plants and insects associated with Leptographium spp. (Jacobs, K.; Wingfield, M.J.; Crous, P.W.; Wingfield, B.D. - ;3.7.53).
Radopholus similis. Radopholus similis (EPPO A2 quarantine pest) occurs in clusters in roots and stems of Anthurium. For quarantine detection purposes, it is recommended to take root samples from middle-aged roots, as the oldest roots are often too decomposed to support nematodes and in younger roots sufficient levels of populations may have not been reached. In addition, its is also appropriate to test stem tissue (Sipes, B. - 2.4.8).
Ralstonia solanacearum. Bacterial wilt of eucalyptus caused by Ralstonia solanacearum (EPPO A2 quarantine pest) was reported for the first time in 1997 in the Kwazulu Natal province, South Africa. R. solanacearum was found for the first time on eucalyptus in Brazil (race 1 biovar 2) in the early 1980s and later on this host in Australia (race 1 biovar 3), China (race 1 biovar 3), Taiwan and Venezuela. In Kwazulu Natal province, R. solanacearum biovar 3 has been identified (Coutinho, T.A.; Wingfield, M.J.; Roux, J.; de Beer, Z.W.; Riedel, K.H.; Esler, C. - 3.7.69).
Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola. Genetic differences between Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola (both A1 quarantine pests) were studied by using PCR-RFLP, sequencing and southern hybridization. Results showed that although they are two distinct bacterium, X. oryzae pv. oryzae and X. oryzae pv. oryzicola are closely related in genetic features as well as phenotypic ones, except for slight differences in the analysis of certain genes (Ochiai, H.; Kaku, H. - 2.2.50).
Xylella fastidiosa. Studies were done in southeastern USA to identify the causes of dieback or decline of American sycamore (Platanus occidentalis) which has been observed for many years. Several pathogens were detected: Xylella fastidiosa (EPPO A1 quarantine pest), Ceratocystis fimbriata f.sp. platani and Botryosphaeria rhodina. Further research is needed to determine whether these pathogens act alone or in combination, and which are the most important in disease etiology (Britton, K.O.; Leininger, T.; Chang, C.J.; Harrington, T.C. - 3.7.50).
Sources
Abstracts of papers presented at the 7th International Congress of Plant Pathology, Edinburgh, GB, 1998-08-09/16.