Biological control of anthracnose of avocado

Anthracnose is a major postharvest disease of avocado in Australia and New Zealand. Current control of this disease relies heavily on the use of fungicides, both before and after harvest. Worldwide consumer concern over the use of pesticides in agriculture has prompted the search for non-chemical alternatives to fungicides for disease control in many horticultural crops. Biological control, using naturally-occurring microorganisms isolated from fruit and leaf surfaces, has been shown overseas to have considerable potential for the control of a range of preharvest and postharvest diseases of tropical fruit including avocado. The aim of this project was to evaluate biological control for anthracnose of avocado

Plant health biosecurity, risk management and capacity building for the nursery industry

Project NY11001 has been a four year funding partnership between the Australian nursery industry, the Queensland Department of Agriculture & Fisheries (DAF), and Horticulture Innovation Australia (HIA). The aim of the project was to provide support to the nursery industry in the area of plant health and biosecurity, including the identification and management of plant diseases and pests through professional diagnostics, skill enhancement of industry through training workshops, and the development of various resources for on-farm biosecurity management

Better understanding epidemiology of Panama disease of banana

This study involved traditional and molecular methods to track the movement of Fusarium oxysporum f.sp. cubense (Foc) in the vascular system of banana. Traditional studies were conducted in the field using naturally-infected Lady finger banana plants, and molecular studies are currently being conducted at UQ using banana plants artificially-inoculated with GFP-transformed Foc isolates in the glasshouse. Panama disease is a polycyclic disease where inoculum causing infection is produced in individual plants infected during the course of the epidemic. This field study clearly demonstrated that the sap produced in such plants will be contaminated with Foc, and will contribute to epidemic build-up if allowed to contaminate the soil. Thus, sap as a source of inoculum is very important when managing disease containment. The study also suggested that the laticifers are not colonised by Foc and that when a pseudostem is cut, the sap from the laticifers is contaminated by inoculum from severed vascular strands and/or associated necrotic tissues. It is difficult to separate these tissues, but results suggest that mycelial fragments may come from severed vascular strands or xylem fluid, and microconidia from necrotic cells adjacent to the vascular bundles. It is anticipated that GFP-transformed isolates being used in the experiment at UQ will provide more definitive evidence on the systemic infection process of Foc in banana. It will determine whether movement in the vascular tissue is via mycelial growth or microconidia, and may explain why the incubation and latent periods for the disease are often so long. Chemical intervention to reduce inoculum levels may be possible but will require much more detailed research. The production of a volatile chemical (bicyclo(4,2,0) octa-1, 3, 5-triene) detected in this study by race 4 strains of Foc in culture is interesting and presents the opportunity for detection of disease by “sniffer” dogs before external disease symptoms are produced. Whether this chemical is produced in infected plants is yet to be determined

Rootstock influences postharvest anthracnose development in 'Hass' avocado

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

Postharvest diseases of mangoes in Fiji

Despite considerable research globally on postharvest diseases of mango, virtually no work has been done to determine the occurrence of these diseases and their causal agents in Fiji. This study is the first major field and market survey of postharvest diseases of mango in Fiji. For the field survey, fruits from five local mango cultivars were harvested at each of five locations. Fruits from five imported cultivars were also harvested from one location in Nadi. For the market survey, vendors were selected at five municipal markets for fruit collection, along with ten roadside stalls. For field and market surveys, fruits were incubated at 23°C and assessed for postharvest disease (incidence and severity of body rots and stem end rots) when ripe. Isolations were made from disease lesions and fungal cultures were identified using multilocus sequence typing. High incidences of body and stem end rots were recorded across all surveys. In the field survey of local cultivars, ?Salusalu? fruits were found to have the lowest severity of body rot and stem end rot on average, while for imported cultivars, ?Nam Doc Mai? had the lowest average severity of these diseases. The market survey showed that ?Salusalu? had a lower incidence of anthracnose on the body of fruit compared to all other cultivars, although it did have a surprisingly high incidence of stem end rot at some localities. Fungal isolates from anthracnose lesions in the field and market surveys were identified as Colletotrichum asianum, C. simmondsii and C. fructicola. C. asianum was the predominant species associated with anthracnose symptoms, accounting for 97% of isolations. Lasiodiplodia theobromae and Neofusicoccum parvum were the predominant species found in association with mango stem end rot symptoms. Other species isolated from mango stem end rot in lesser numbers included L. brasiliensis, N. umdonicola and N. kwambonambiense. All of these fungi represent new reports for Fiji

The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

Lychee pepper spot, a field disease affecting lychee fruit skin, pedicels and petioles, is caused by Colletotrichum siamense, a fungal pathogen within the gloeosporioides species complex. Members of Colletotrichum from the gloeosporioides species complex and occasionally those from the acutatum species complex also cause postharvest anthracnose of lychee. Pepper spot was first described in Australia many years after anthracnose on lychee was first described, giving rise to the hypothesis that a novel species or strain within the gloeosporioides species complex causes pepper spot. In the present study, 19 isolates of Colletotrichum spp., collected from pepper spot and anthracnose symptoms on lychee fruit, representing 13 different genotypes across five species, were inoculated onto lychee fruit in the field or on detached fruit in the laboratory, to understand more about their pathogenic diversity. We found that symptoms were specific to genotype of the pathogen, as three genetically similar isolates of C. siamense consistently caused pepper spot and anthracnose, whilst other isolates caused anthracnose only. Cross-inoculation studies on detached fruit of lychee, banana, avocado and mango also provided some evidence of host specialization in isolates of C. siamense infecting lychee in Australia. Our experiments provided further evidence that detached fruit assays cannot be used as a reliable proxy for field inoculation studies. This research confirms that C. siamense is a causal agent of both lychee pepper spot and lychee anthracnose in Australia, and Colletotrichum alienum and Colletotrichum queenslandicum are reported as causal agents of anthracnose of lychee for the first time