Characterisation of Botrytis species associated with neck rot of onion in Australia
Neck rot of onion has commonly been attributed to two fungal pathogens, Botrytis aclada (syn. B. allii) and B. byssoidea. However, in other countries, a recently developed PCR technique using sequence characterised amplified region (SCAR) primers (BA2f/BA1r) followed by ApoI digestion of the amplification product, has shown the presence of two groups within B. aclada, B. aclada AI and B. aclada AII syn. B. allii. This method was used to characterise Botrytis spp. of the B. aclada/B. allii complex associated with onion seed and bulbs in Australia. A total of 24 Botrytis isolates, including two from seed and ten from bulbs (Tasmania), five from seed (South Australia), and one from seed and six from a culture collection originally isolated from five bulbs and one stipe (New South Wales), were characterised. Of the 24 isolates, one was identified as B. cinerea, one as B. aclada AI, and 22 as B. aclada All syn. B. allii.
Origin of a polyploid Botrytis pathogen through interspecific hybridization between Botrytis aclada and B. byssoidea
Abstract Botrytis aclada has previously been divided into two subgroups (AI and AII) based on spore size, chromosome number and genetic markers. A recent study of genetic diversity using universal-primed PCR (UP-PCR) fingerprints showed that subgroup AII of B. aclada was a possible hybrid species between B. byssoidea and subgroup AI of B. aclada. To test this hypothesis, we sequenced a UP-PCR fragment (~550 bp) from representative isolates of four Botrytis species, all causing disease on onions. A mixture of two nucleotides at each nucleotide position was found in all AII isolates analyzed at 23 positions in the sequence. These isolates had 32 chromosomes, whereas all AI isolates had 16 chromosomes. Pair-wise comparison of the sequences of the four Botrytis species showed that a hybridization event between B. aclada (AI) and B. byssoidea could explain all 23 positions with mixed nucleotides, supporting them as being parental ancestors to AII. These results indicate that at least one Botrytis pathogen has evolved through interspecific hybridization.
Methods for inducing sporulation of some Botrytis species occurring on onions and leeks
Methods were developed to induce and accelerate sporulation in Botrytis allii, B. byssoidea, B. cinerea and B. squamosa. The effects of temperature (5–20°C), substrate (prune, lactose, yeast, streptomycin, erythromycin agar (PLYSE), onion leaf and bulb tissue) and light (darkness, white fluorescent and near ultraviolet light (n.u.v.)) on spore production were tested. B. allii sporulated best at 20° on PLYSE under n.u.v.; B. cinerea at 15° on PLYSE under n.u.v. ; B. byssoidea at 15° on PLYSE under n.u.v., or on onion bulb tissue at 20° under n.u.v. ; B. squamosa sporulated slowly on agar at 5° on PLYSE under n.u.v. and faster on leaf tissue at 15° under alternating 12 h white fluorescent light and dark.