Soybean breeding for parasite resistance

Abstract

Large epidemics may cause significant damage to soybeans. Long-term observations have indicated that Peronospora manshurica (downy mildew), Pseudomonas syringae pv. glycinea (bacterial spot), Sclerotinia sclerotiorum (white rot), Diaporthe phaseolorum var. caulivora (stem canker) and Phomopsis longicolla (seed decay) are the most widely distributed and most harmful soybean diseases in Serbia. Soybean crop may be successfully protected by a combination of measures among which the development and utilization of resistant cultivars is most efficient, most economic and ecologically most acceptable. The populations of P. manshurica and P. syringae pv. glycinea, the parasites of soybean leaves, vary in virulence rate, i.e., there are several physiological races of these fungi. In the case of Diaporthe/Phomopsis, however, variation in virulence rate has been observed, but physiological races have not been identified. Success in breeding of resistant cultivars depends on the existence of effective sources of resistance, as well as on the nature and mode of inheritance of resistance. There are several sources of resistance to P. manshurica, which mostly contain one dominant, major gene (Rpm). These sources thus provide complete resistance, however, it is not lasting but becomes lost with time. Our efforts are centered on widening the genetic basis of resistance, by accumulating several resistance genes from different sources. Race 4 of P. syringae pv. glycinea is dominant in soybeans around the world as well as in our country. There is no genotype completely resistant to this race, but there exist significant differences in the rate of susceptibility. Partial resistance is controlled by one or several Rpg genes. A collection of resistant and less sensitive soybean genotypes has been established at Institute of Field and Vegetable Crops in Novi Sad. These materials have been included in soybean breeding programs. Mechanisms of disease escape and partial physiological resistance bring differences in soybean reaction to S. sclerotiorum. Two loci controlling disease escape mechanisms and one locus most probably responsible for partial physiological resistance have been mapped. Partial resistance has been found in several introduced (PI) soybean cultivars. Under the local conditions, early genotypes are less sensitive that late ones. Complete resistance to D. phaseolorum var. caulivora, the agent of stem canker, has not been registered. Late genotypes are very sensitive to stem canker, while early cultivars and lines manage to avoid the parasite's attack under the local agroecological conditions. Species from the genus Diaporthe/Phomopsis are the most harmful parasites of soybean seed. Resistance to them is controlled by a single dominant gene, which has been registered in several soybean genotypes. The early domestic cultivars are more sensitive to the disease than the late ones. It should be mentioned here that much has been done on the introduction of resistance to Phytophthora megasperma f. sp. glycinea into commercial cultivars, especially in the USA.

Daje se pregled rezultata rada oplemenjivanja soje na otpornost prema parazitima u svetu i kod nas. Detaljnije su obrađeni najštetniji paraziti u Srbiji, i to: Peronospora manshurica (plamenjača), Pseudomonas syringae pv. glycinea (bakteriozna pegavost), Sclerotinia sclerotiorum (bela trulež), Diaporthe phaseolorum var. caulivora (rak stabla) i prouzrokovači truleži semena iz roda Diaporthe/Phomopsis. Konstatovano je da je stvaranje i gajenje otpornih sorti najefikasnija, najekonomičnija i ekološki najbezbednija mera zaštite. Ukazano je na fiziološku specijalizaciju pojedinih patogena (fiziološke rase), naročito izraženu kod P. manshurica i P. syringae pv. glycinea, što uslovljava da proces oplemenjivanja na otpornost mora biti kontinuiran. Navedeni su otporni, parcijalno rezistentni i manje osetljivi genotipovi soje prema pojedinim parazitima, koji se koriste u procesu oplemenjivanja. Korišćenje molekularnih markera, odnosno, mogućnost mapiranje gena, znatno je doprinelo boljem poznavanju prirode otpornosti i načina nasleđivanja otpornosti prema parazitima. U tom pogledu najveći napredak je napravljen kod S. sclerotiorum, P. longicolla i P. syringae pv. glycinea, parazita prema kojim nije evidentirana potpuna, već parcijalna rezistentnost. Treba istaći da je najviše rađeno na unošenju otpornosti prema Phytophthora megasperma f. sp. glycinea u komercijalne sorte, naročito u SAD. Inače, ovaj parazit nije prisutan na soji u Srbiji.