Characterisation and early detection of an offtype from micropropagated Lady Finger bananas

An offtype has been identified from micropropagated Lady Finger bananas (Mu sa spp., AAB group, Pome subgroup) that is characterised by its slow growth and poor bunch size. Bunch weights were approximately 25% those of normal Lady Finger plants and all of the fruit produced was unmarketable. This par ticular offtype is the most commonly encountered from micropropagated Lady Finger plants and, in 2 instances, blocks of 3000 and 1500 plants were enti rely comprised of this single offtype. Detection of offtype plants was possible during establishment and growth of plants in the glasshouse by the presence of chlorotic streaks in the leave s. In more severe cases the streaks coalesced into chlorotic patches that d eveloped thin, necrotic areas that eventually produced holes or splits in t he leaves. Symptom expression was not ameliorated by the addition of fertil iser and even though symptoms were similar to severe Ca and B deficiency, b oth normal and offtype plants had similar levels of these elements in the l eaves. The offtype plants were also slow growing in the glasshouse and prod uced significantly (P<0.05) smaller pseudostems and leaves than normal plan ts. Offtype plants could be readily detected after 4 weeks deflasking using the presence of chlorotic streaks in the leaves as the main selection crit erion. Maximum discrimination was possible between weeks 5-7 and at the 6-l eaf stage when all of the offtypes could be detected.