Predicting Broccoli Development: I. Development Is Predominantly Determined By Temperature Rather Than Photoperiod

Predictive models of broccoli (Brassica oleracea L. var. italica Plenck) ontogeny will aid farmers who need to forecast changes in crop maturity arising from variable climatic conditions so that their forward marketing arrangements can match their anticipated supply. The objective of this study was to quantify the temperature and photoperiod responses of development in a sub-tropical environment from emergence to floral initiation (EFI), and from floral initiation to harvest maturity (FIHM). Three cultivars, ('Fiesta', 'Greenbelt' and 'Marathon') were sown on eight dates from 11 March to 22 May 1997 and grown under natural and extended (16 h) photoperiods at Gatton College, south-east Queensland, under non-limiting conditions of water and nutrient supply. Climatic data, dates of emergence, floral initiation and harvest maturity were obtained. The estimated base (Tbase) and optimum (Topt) temperatures of 0 and 20 degrees C, respectively were consistent across cultivars, but thermal time requirements were cultivar specific. Differences in thermal time between cultivars during FIHM were small and of little practical importance, but differences in thermal time during EFI were large. Sensitivity to photoperiod and solar radiation was low in the three cultivars used. When the thermal time models were tested on independent data for five cultivars ('Fiesta', 'Greenbelt', 'Marathon', 'CMS Liberty' and 'Triathlon') grown as commercial crops over two years, they adequately predicted floral initiation and harvest maturity

Rootstocks influence 'Hass' avocado fruit quality and fruit minerals

To determine the potential for rootstocks to improve avocado quality, 'Hass' fruit from trees on seedling 'Velvick' (SV), clonal 'Velvick' (CV) or clonal 'Duke 7' (CD) rootstocks were harvested in 1999 and 2000, ripened at 20 C immediately after harvest (non-stored) or stored at 5 C for four weeks (stored), and then fruit quality and mineral concentrations determined. In 2000, non-stored CV fruit had lower severity of body rots (5% of flesh volume affected, caused mainly by Colletotrichum gloeosporioides) than CD fruit (20%), while body rots severity in stored CV fruit was 20% compared with 38% in stored CD fruit. Stored CV fruit had less severe diffuse discoloration (3% and 9% in 1999 and 2000, respectively) than CD fruit (7% and 20%, respectively). Stored CV fruit also had less severe vascular browning (19%) than CD fruit (33%) in 2000. In both seasons, CV fruit had 15-19% higher flesh calcium concentrations, 17-22% higher flesh boron concentrations, and 14-15% lower flesh nitrogen concentrations than CD fruit. In 2000, CV fruit also had 27% more skin calcium and 14% less skin nitrogen than CD fruit. There were no effects of rootstock on yield, canopy volume, measured length of non-suberized roots, average fruit weight, fruit length: width ratio, skin thickness, dry matter, proportion of the fruit skin purple-black when ripe, or seed mass: fruit weight ratio. These results suggest that there is potential to improve 'Hass' avocado quality through rootstock selection, and that tree and fruit mineral concentrations have a role in this relationship

Activating Mango Fruit Defence to Anthracnose Disease

The fungus causing anthracnose disease in mango, Colletotrichum gloeosporioides, (C g.), infects immature fruit early in the season, then enters a long latent phase. After harvest, when fruit start to ripen, the latency breaks and the fungus ramifies through the peel and pulp tissues causing black disease lesions. The breaking of pathogen latency in ripening mango fruit has been correlated with decreasing concentrations of the endogenous antifungal resorcinol compounds (Droby et al., 1986). The level of these antifungal resorcinols vary among mango cultivars (Droby et a1 , 1986). Controlling diseases by managing natural resistance of fruit to fungal attack could minimize the use of pesticides, which have become of major public concern on health and environmental grounds. The plant resistance activator benzo(l,2,3)thiadiazole-7-carbothioic acid S-methyl ester (trade name Bion®) has been widely reported as an effective inducer of systemic resistance. For example, Bion® was reported to induce pathogenesis-related proteins (PR proteins) and stimulate plant defence in peas (Dann and Deverall, 2000) and roses (Suo and Leung, 2001). However, until now, there is no information about the role of Bion® in activation of mango (cv. Kensington Pride) fruit resistance to anthracnose disease. The aim of this research is to determine the effect of resistance activators on defence responses of mango fruit to anthracnose disease

Alk (en) ylresorcinol concentrations in'Kensington Pride'mango peel and antifungal activity against Colletotrichum gloeosporioides

Two preformed alk(en)ylresorcinols, 5-n-heptadecenylresorcinol and 5-n-pentadecylresorcinol, were identified in ‘Kensington Pride’ mango fruit peel. The alk(en)ylresorcinols had antifungal activity against C. gloeosporioides, as determined from thin layer chromatography bioassays. Soil-applied activators of plant defence (Acibenzolar at 150 mg L-1, and soluble potassium silicate at 200 and 1000 mg L-1) did not influence concentrations of 5-n-heptadecenylresorcinol or 5-n-pentadecyl¬resorcinol in mango peel when applied 2 months after fruit set and one month later. Concentrations of both alk(en)ylresorcinols were high 2 months after fruit set but levels declined by 50% within 1 month (2 months before commercial harvest) and did not change significantly from commercial harvest until eating-ripe