SummaryThe stem end rot pathogens of mango (Mangifera indica), (Dothiorella dominicana, Dothiorella mangiferae, Lasiodiplodia theobromae (Syn. Diplodia natalensis Phomopsis mangiferae, Cytosphaera mangiferae, Pestalotiopsis sp. and Dothiorella‘long’), as well as other fungi (including Alternaria alternata), were found to occur endophytically in the stem tissue of mango trees prior to inflorescence emergence. On samples from trees with a record of low stem end rot levels, colonisation did not extend into the most recently produced flush of stem tissue. At a site with a history of high stem end rot levels, sequential monitoring of inflorescence tissue between flowering and harvest by plating out small (c. 8 mm3) tissue pieces revealed, that at least some of the pathogens ‐ Dothiorella spp., P. mangiferae, Pestalotiopsis sp. and C. mangiferae gradually colonised the inflorescence, reaching the pedicel tissue of young fruit ‐ 8 wk after flowering. Subsequently, detection frequency of the pathogens in inflorescence tissue declined, possibly because of interference from copper residues (from field sprays) accumulating on tissue samples. The detection frequency of A. alternata also increased as Dothiorella spp. declined, however these changes could not be attributed to antagonistic interactions between the two fungi.Using larger tissue pieces (1–2 mm thick transverse sections, or a square of tissue 25 mm2× 3 mm thick) in isolations, endophytic colonisation by Dothiorella spp. and P. mangiferae was detected in stem, inflorescence and pedicel tissues of mature‐fruit‐specimens from two different sites, one unsprayed, and the other regularly sprayed with copper. The fungi were detected more frequently in the samples from unsprayed trees. Fruit from the sprayed orchard subsequently developed a high level of stem end rot caused by D. dominicana, while a lower level of stem end rot developed in unsprayed fruit, possibly because the latter fruit were also extensively diseased by anthracnose (Colletotrichum gloeosporioides Penz.). Endophytic colonisation of inflorescence and pedicel tissue was found to be a primary route of infection for fruit which develop stem end rot during ripening.

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Rootstock studies conducted on ‘Hass’ avocado found that rootstock had a significant impact on postharvest anthracnose susceptibility. This is the first record of such an effect for avocado. The severity and incidence of anthracnose was significantly lower on ‘Hass’ grafted to ‘Velvick’ Guatemalan seedling rootstock compared with the ‘Duke 6’ Mexican seedling rootstock. Differences in anthracnose susceptibility were related to significant differences in concentrations of antifungal dienes in the leaves and mineral nutrients in the leaves and fruits from trees grafted to different rootstocks. Leaf diene concentrations were up to 1.5 times higher in ‘Hass’ trees on the ‘Velvick’ than the ‘Duke 6’ rootstock. In ungrafted nursery stock trees, diene concentrations were around 3 times higher in ‘Velvick’ than ‘Duke 6’ leaves. The ‘Velvick’/‘Hass’ combination also had a significantly lower leaf N concentration, a significantly higher fruit flesh Mn concentration, and significantly lower and higher leaf N/Ca and Ca+Mg/K ratios, respectively. A significant correlation (r = 0.82) between anthracnose severity and skin N/Ca ratio was also evident.

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Calonectria ilicicola, Gliocladiopsis sp. and Ilyonectria liriodendri were isolated from diseased roots of young avocado trees. Pathogenicity studies with seedlings of three avocado cultivars, Velvick, Hass and Reed, demonstrated that Calonectria ilicicola is a severe root rot pathogen, reducing the biomass of healthy roots, and reducing plant height over time. Calonectria ilicicola was re-isolated from diseased roots. Ilyonectria liriodendri and Gliocladiopsis sp. were not pathogenic and plant height was increased after Gliocladiopsis sp. amendment compared to all other treatments in trials with cvs Velvick and Hass.

The disease control efficacy of quarantine heat treatments developed for fruit fly disinfestation in mangoes cv. Kensington Pride was evaluated in this study. Heat was applied using high humidity (>95% r.h.) hot air (HHHA) at temperatures ranging from 4749°C.Anthracnose, caused by Colletotrichum gloeosporioides, was well controlled in mangoes heated to a core temperature of 46"C, 47°C or 48°C for 24, 10 or 8 min respectively, prior to ripening at 23°C for 16 days. Stem end rot, caused by Dothiorella dominicana and Lasiodiplodia theobromae, was not satisfactorily controlled by these treatments.In a subsequent experiment, fruit were immersed in a hot benomyl(0.5 g a.i. litre-' at 52°C for 5 min) or unheated prochloraz (0.25 ml a.i. litre-' at 28°C for 30 s) dip before or after the application of HHHA (core temperature of 47°C for 10 min). During storage at 23°C for 15 days, the incidence of stem end rot was reduced by HHHA alone, although immersion in hot benomyl either before or after HHHA treatment greatly improved stem end rot control.HHHA treatment (core temperature of 465°C for 10 min) alone reduced the incidence of anthracnose in mangoes stored at 13°C for 14 days prior to ripening at 22"C, although a combination treatment consisting of HHHA and either hot benomyl or unheated prochloraz gave complete control of anthracnose under these storage conditions. HHHA treatment alone gave no control of stem end rot in mangoes stored at 13°C prior to ripening at 22°C. A supplementary hot benomyl treatment was required for acceptable control of this disease in coolstored mangoes. The development of yellow skin colour in fruit was accelerated by HHHA treatment.

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During flowering and fruit set of mango (Mangifera indica L.), colonisation by fungi (Alternaria alternata, Cladosporium cladosporioides, Dothiorella dominicana, Dothiorella mangiferae, Dothiorella sp., Epicoccum purpurascens and Pestalotiopsis sp.) increased as the flowers senesced and young fruit formed.In the third week after flowering, the incidence of Dothiorella dominicana and Dothiorella mangiferae associated with mango fruit-pedicel connection tissue declined coincidentally with early fruit-fall, suggesting that early infections by Dothiorella spp. may cause fruitlet abortion. Dothiorella spp. levels in fruit-pedicel connection tissue remained low for the subsequent 6 weeks, after which they increased. By 16 weeks after flowering, the incidence of Dothiorella spp., determined by isolation from fruit-pedicel connection tissue, was similar to the incidence of stem end rot caused by Dothiorella spp., which developed in fruit harvested at that time. By contrast, the frequency of detection of Dothiorella spp. in peduncle tissue peaked 11 weeks after flowering, when the levels of stem end rot developing in fruit were already similar to the levels recorded in fruit harvested at 16 weeks and later.The results suggest that in fruit and fruit-pedicel tissue, colonisation might arise from Dothiorella spp. occurring endophytically in the peduncle. The earliest indicator of stem end rot incidence at harvest was the infection level in peduncle tissue sampled 11 weeks after flowering. Early assays of peduncle tissue for Dothiorella spp. might prove useful for selecting crops with low stem end rot infection levels.