Screening for resistance to Diaporthe toxica in lupins by estimation of phomopsins and glucoseamine in individual plants

Immunological and biochemical assays were developed for screening for resis tance to Diaporthe toxica in individual plants of narrow-leafed lupins (Lup inus angustifolius). The former was an enzyme-linked immunosorbent assay (E LISA) for measuring phomopsin mycotoxins and the latter gave an estimation of glucoseamine in infected stem pieces. Stems of L. angustifolius seedling s were inoculated with conidia from D. toxica cultures and, as expected wit h this latent disease, remained symptomless for 21 days after inoculation. At this time, phomopsins were measured in excised stems that had been incub ated for 6 or 8 days to allow mycelial growth from latent infection structu res, thereby increasing the phomopsins to detectable levels in individual p lants. The estimation of glucoseamine was carried out on the same stems tha t had been assayed for phomopsins. The method was based on the alkaline dea cetylation of chitin to chitosan, the glucoseamine residues of which are de -aminated with nitrous acid, yielding an aldehyde which is determined color imetrically. At six days after excision, both tests clearly distinguished t he very resistant, resistant, intermediate and susceptible lines and they m ay be useful in large-scale resistance screening in lupin breeding programm es. The ELISA of phomopsins is easier to use and would be particularly usef ul in the elimination of susceptible plants and those plants expressing int ermediate levels of resistance during early generations of the breeding pro gramme.