R. J. Collins’s research while affiliated with University of Queensland and other places

A series of experiments was conducted to evaluate the nutritional requirements of non-astringent persimmon in subtropical Australia. Three rates and two times of application of the two major nutrients, N and K, were evaluated for two different soil types in south-east Queensland. Nitrogen and K were shown to be key manipulators of productivity. At both low (<40 kg per hectare) and high (>100 kg per hectare) annual rates of N, the total number of fruit per tree was reduced due to adverse effects on fruit set and increased fruit drop. With potassium, average fruit weight and yield increased with increasing rates of K applied up to 80 kg per hectare, and much more slowly thereafter. Multiple, sequential foliar applications of Ca were shown to increase leaf Ca concentrations by 20%, improve fruit firmness and storage life. A benchmarking survey of leading orchards was also undertaken to document current nutritional practices, and to determine if there was a relationship between leaf nutrient concentrations with productivity. Salinity was a major problem in some production regions; and at leaf Cl concentrations above 0.8%, yield was severely reduced. Based on these studies, a new, narrower range of leaf nutrient standards at both fruit set and one month prior to harvest is being developed.

Traditional production systems for growing non-astringent persimmon throughout the world have changed rapidly in the last 10 years. New systems have been developed to grow persimmon in subtropical regions of the world. In Australia most orchards are now trained to a palmette system rather than the conventional vase shape system, allowing for easier management and growth control. In contrast, in New Zealand trees are trained to a Y trellis system to improve light interception under cloudy growing conditions. Reflective mulch is also used to further maximise light use and increase fruit heat units necessary to fully mature the fruit. Tree plantings densities have increased from 400 to 800 trees per hectare. In Japan high density plantings using micro-propagated trees are being evaluated. In Australia many orchards are netted to exclude birds and fruit eating bats. Multi-purpose fruit fly exclusion netting is also being evaluated as an environmentally friendly alternative to insecticidal cover sprays. New formulations of fruit fly bait sprays with greater efficacy and longer field life have also been developed. Sporadic and erractic budbreak can be a major problem in subtropical regions where trees do receive sufficient chilling. A new range of rest-breaking chemicals such as Armobreak (akolated amine) and Waiken (fatty acid esters) can increase the percentage budbreak, flowering and yield. Excessive vegetative growth during the flowering period leads to competing sinks, reducing fruit set and fruit size. The growth retardant paclobutrazol has been shown to effectively control growth reducing tree size by about 20%. Paclobutrazol also advanced the harvest period by about 2 weeks without loss of fruit quality or storage life. Attempts at improving fruit firmness and post-harvest shelf life through foliar application of Ca have been partially successful but multiple sequential applications are necessary to be effective. Preliminary studies have shown that a new group of growth regulators, ethylene biosynthesis inhibitors, when applied 2 to 3 weeks prior to harvest, delayed fruit maturity and improved fruit size, firmness and storage life

Three surveys were conducted to determine the most commonly used cultivars and management practices across Australia. The persimmon industry is established from the semi-tropical far north of Queensland to the cool temperate zones of Victoria, South Australia and Western Australia. Fruit from warmer regions mature four months earlier, giving a harvest spread from February to June inclusive. The majority of the Australian industry is based on the non-astringent cultivar Fuyu. Only 26% of Australian orchards are planted with pollinizers. Yield and fruit size vary within and between regions. Factors contributing to lower yields and smaller size grades are temperature, salinity, pollination, and training and management systems. The most common tree training system is the freestanding vase, followed by palmette, the V- and Tatura trellises. Ruakura trellis is the least used. Trellised trees produce higher yields of marketable fruit through increased planting density, improved light interception and a tree structure that stabilises against tree movement, significantly reducing fruit blemish.

Non-astringent persimmon is rapidly expanding as a new fruit crop in warm subtropical regions of the world. Most research and development of this fruit crop has occurred in Japan, where there is a considerable amount of published literature on its performance. Much of this information is not readily accessible to other countries and needs to be interpreted and modified for other climatic regions. This paper reviews reproductive events from floral initiation to the completion of fruit growth. The timing and significance of these events is described in relation to the phenological cycle. Method of improving flowering, reducing fruit drop and altering the fruit maturity period are discussed.

Blemishing is a major quality defect of persimmon both in Australia and New Zealand. Several studies were conducted on the incidence and development of blemish in 4 well-managed orchards in both countries. Over 10 different types of blemishing were identified and documented. Of the blemishes identified, wind rub caused the greatest reduction in marketable fruit. The occurrence of this disorder was 5 times higher in Australia than in New Zealand in spite of windrun in New Zealand being 2–2.5 time higher than in Australia. The lower incidence of wind rub in New Zealand appears to be due to the use of Y trellising, whereas, in Australia, trees are free-standing. The incidence of sunburn varied markedly with season. The incidence of this disorder was reduced by bird-netting (5-15% shade factor) which is the standard management practise in Australia. Line, apex and concentric cracking were minor problems in most orchards. Methods for controlling blemishing in commercial orchards are outlined.

Seasonal changes in net carbon dioxide assimilation (A) were measured over 2 season in a high-yielding ‘Fuyu’ orchard at Palmwoods, Queensland, Australia. Similar patterns of A were recorded in both seasons with only one peak, occurring between 8-11 weeks after full bloom. The peak in A appears to coincide with the period of maximum root growth and stage II of fruit growth. A rates were positively correlated with leaf N (r = 0.85, P<0.05), and moderately negatively correlated with leaf starch (r = -0.82, P <0.05) and specific leaf weight (r = -0.58, P<0.05), indicating an inhibitory feedback mechanism. Specific leaf weight and leaf starch were highly positively correlated (r=0.92, P<0.05). The study suggests that maintaining leaf N within a desirable critical range may be important for maximising fruit growth and for the accumulation of starch reserves for next season crop.

Non-astringent persimmons have a natural tendency to set heavy crops of small fruit followed by light crops of large fruit. Markets discriminate against small fruit. In cooler climates, there are guidelines for removing (thinning) some fruitlets after flowering, a practice that significantly dampens swings in the crop cycle. However, no corresponding guidelines exist for the sub-tropics. Over two years we applied four thinning treatments to 0, 5, 10 and 15 fruit per square metre of canopy surface area on Fuyu persimmons grown in south east Queensland. Tree performance was measured by fruit size and number, as well as by renewal growth and starch reserves in the following season. Trees with highest fruit loads (15 fruit/square metre) produced higher yields of small fruit in the first season followed by lower yield of larger fruit in the next season. They also had lower starch reserves at the beginning of the second season. In contrast, trees with the lowest loads (5 fruit/square metre) produced low yields of large fruit in the first season followed by higher yields of smaller fruit. They had higher starch reserves at the beginning of the second season. Thus non-astringent persimmons in both the sub-tropics and cooler climates respond similarly to thinning, largely because crop load influences starch reserves in the tree in the following season. Our tentative recommendation is to thin Fuyu in the sub-tropics to 10 fruit per square metre.

The influence of canopy position (sectors: N, S, E, W; tree height: top, middle and base) and shoot growth on fruit set, yield and fruit quality of the non-astringent persimmon cultivar 'Fuyu' trained to standard modified central leader system was evaluated in subtropical Australia (Lat. 26° S). The main aim of the study was to determine if different sections of the tree canopy produce greater quantities of export-quality fruit. Light interception, net CO2 assimilation, leaf nutrients, and starch were also measured for each canopy position. Generally, there was little or no effect of canopy position on fruit quality. In contrast, initial fruit set was highest in upper parts of the tree canopy exposed to higher irradiance. Weight of fruit removed from any position was primarily dependent on fruit set at that position. Fruit weight was poorly correlated (r < 0.30, n.s.) with leaf area, leaf number per fruit, shoot length, and shoot base diameter of fruiting shoots indicating that these variables are not useful criteria for determining thinning levels or final fruit size. The fruit disorder, calyx cavity, was least in the middle canopy. In contrast, average fruit weight, Brix, colour, texture and flavour were only slightly affected by canopy position. It was concluded from the study that, in Australia, light influences yield but not fruit quality. Export-quality fruit can be harvested from any position within the tree canopy.

A factorial combination of three cultural factors (± hand-pollination, ± growth retardant, ± fruit thinning) were evaluated for their effects on fruit set and fruit size of ‘Fuyu’ persimmon (Diospyros kaki L.) in subtropical Australia (Lat. 27° S). Treatments were applied to individual shoots on mature seven year old trees. Fruit set of pollinated flowers was high compared with non-pollinated flowers (91% vs. 47%). Pollinated fruit also grew faster at all stages of fruit development and, at harvest, fresh weights were 25% heavier. Palcobutrazol significantly (P<0.05) increased fruit weight by 7% compared with controls but did not increase fruit set. Irrespective of treatment, fruit weight was not correlated (r<0.3, n.s.) with shoot length, number of nodes per shoot, fruit nodal position, shoot dry weight, leaf area per shoot, and number of leaves per shoot. Fruit fresh weight was only poorly correlated with shoot base diameter (r = 0.41*). Pollinated fruit had significantly (P<0.05) higher concentrations of nutrients (N, K, Ca, and Zn).