During 1978-80, flower emergence was recorded on 12 almond cultivars (Prunus dulcis) at Angle Vale, South Australia. Early flowering cultivars showed a larger annual variation in flowering period (2-3 weeks) than late flowering cultivars (0-2 weeks). In the same period, pollen production ranged from 30 to 122 mg per 100 flowers and in vitro pollen germination ranged from 76.1 to 99.0%. Pollen production and in vitro germination differed significantly between cultivars. Hand-pollination of Nonpareil with pollen from each of eight other cultivars resulted in significantly higher nut set than with open-pollinated or self-pollinated flowers. In contrast to Nonpareil, hand-pollination of Chellaston with pollen from five other cultivars resulted in significantly higher nut set compared with self-pollinated Chellaston but not compared with open-pollinated Chellaston. The potential increase in almond yield due to improved pollination is discussed.
Records of flowering in 12 almond cultivars over 7 years, together with temperature records from a standard climate station, were used to estimate the chilling requirement for dormancy break in flower buds and the heat sum requirements for floral development in each cultivar. Hourly temperatures were estimated from daily minimum and maximum temperatures. A continuous function relating hourly temperatures to rate of chilling was used to calculate daily chill unit accumulations. Requirements of 220-320 chill units were estimated and calculated heat sum requirements ranged from 5300 to 8900 growing-degree-hours above 4-5�C. These requirements were used to estimate the dates of 50% flowering for 1958-84.
A model for the prediction of flowering date in almond requires estimates of the chilling and heat sum requirements. We estimated hourly temperatures from daily minimum and maximum temperatures. A continuous function relating hourly temperature to rate of chilling was used to calculate daily chill unit accumulations. Heat sums were measured as growing-degree-hours: the linear accumulation of hourly temperatures above a threshold temperature. Our model was tested with estimates derived from data obtained at 1 French and 2 Australian locations. The results indicate that estimates derived from data at a single location can be successfully used for other locations with different climates. The accuracy of flowering date prediction generally improves as the number of locations and years of data on which it is based increase. The predictions for the cultivars Mission and Nonpareil were within 5 days of the observed dates in 73 and 88% respectively of the locations-years examined. We concluded that the chilling requirement in almond is (mean � s.e.) 284 � 33 chill units and 3 groups of cultivars can be identified with respect to heat sum requirement in the ranges 5300-6300; 6800-7700 and 8200-8900 degree hours above 4.5�C.
Eight Nonpareil almond clones on Nemaguard rootstock were yield-tested in a field trial at Irymple, Victoria, for 4 cropping seasons (1986-89). Although few significant differences in yield were recorded in any year, the results showed that the Nonpareil clones differed in total yield and in total yield per unit of butt cross-sectional area by as much as 50%. For example, clone L54/3 produced a total dry kernel yield per tree per unit of butt crosssectional area of 51.2 kglcm2, while the high yielding clone G11/16 produced a yield of 77.6 kg/cm2. The 3 top-yielding clones (GI 1/16, P7/29 and K5/7) produced total dry kernel yields (1986-89) per tree per unit of butt cross-sectional area of 77.6, 73.6 and 71.7 g/cm2. However, clone K5/7 proved to be subject to non-infectious bud failure, and it is concluded that clones G11/16 and P7/29 could be useful, high-yielding clones for the Australian almond industry.
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