Since the physiological mechanisms responsible for yield losses under dry conditions are unknown, especially for grain crops, we attempted to identify them in maize (Zea mays L.) subjected” to a water deficiency during most of the grain filling period. The plants were grown in a controlled environment capable of providing yields comparable to the field. Grain yield, dry weights of shoots and roots, apparent photosynthesis, and leaf water potentials (Ψw) were determined. Shortly after tasseling, water was withheld from the soil of half the plants until Ψw had decreased to —18 to —20 bars, where Ψw remained until maturity. Apparent photosynthesis became virtually zero at these Ψw. However, grain yield was 47 to 69% of the control yield. At low Ψw, the grain developed partly at the expense of photosynthate accumulated prior to the desiccation period. Since grain development is dependent entirely on translocation in maize, this indicated that translocation continued despite the cessation of apparent photosynthesis. The parameter most closely related to yield was dry matter accumulated during the entire growing season rather than that accumulated during grain fill alone. We conclude that translocation it less inhibited than photosynthesis during drought, and that the total photosynthetic accumulation for the growing season controls yield during a drought that does not disrupt the flowering process.

Measurements of the timing and amount of budbreak and flowering in 'Hayward' kiwifruit were made over 4 years in six regions of New Zealand. There was a large variation in the vine attributes measured. The number of flowers produced/winter bud varied 5-fold between the worst site-year combination and the best. The time of 50% budbreak varied by 32 days and the time of 50% flowering by 25 days. The proportion of flowers on the distal (tip) two buds ranged in a single year from a low of 10% at one site to > 65% at another on canes which had an average of 21 buds. The number of flowers/winter bud is considered to be made up of four components: the proportion of budbreak, the proportion of floral buds, the number of inflorescences/floral bud, and the number of flowers/ inflorescence. The proportion of budbreak and the proportion of floral buds were found to be most important in determining the number of flowers produced/winter bud, and both of these components were significantly higher at the cooler, southern, sites. The vines measured in this survey were all H93053 chosen from a single block in a single orchard within each region, so between-vine variation was minimised. Despite this, total between-vine variation accounted for nearly 40% of the observed variance in the proportion of budbreak and about a quarter of the observed variance in the number of flowers/ winter bud and the proportion of floral buds. Differences between regions were significant for all vine attributes measured except the number of inflorescences/floral bud, with cooler sites generally breaking bud earlier and producing more flowers. When averaged over all 4 years, the number of flowers/winter bud was over twice as high at the coolest site than at the warmest, and budbreak occurred more than 3 weeks earlier. The proportion of flowers on the tip two buds varied from an average of < 17% at one site to > 50% at the warmest site. Year-to-year differences were generally not significant when averaged over all regions, except that flowering tended to be early or late at all sites in the same years. Year-to-year variation was however very important within each region. Over 50% of the variance in the number of inflorescences/ floral bud was the result of year-to-year variation, and over a third of the variance of the number of flowers/winter bud. At the warmest site, both the number of flowers/winter bud and the proportion of flowers borne by the tip two buds varied more than 2-fold in consecutive years. It is this betweenseason variation that is of major significance in orchard management. It is also important for the industry at large because of the need to organise transport, storage, and marketing on a region-byregion basis.

The results of controlled environment experiments and a field survey covering six major New Zealand kiwifruit (Actinidia deliciosa) growing regions over 3 years showed, surprisingly, that the effect of temperature on the rate of fruit growth is small, at least during the second half of the fruit growth period. The considerable variation in the mean and standard deviation of fruit volume at harvest observed in the field among seasons and sites is therefore not attributable to temperature differences during the fruit-growing season. This raises the possibility that most of the factors affecting fruit growth rates may be established early in the season, so harvest fruit volumes can be predicted from early-season measurements. Mean fruit volumes observed in the field survey ranged from <85 ml (Kerikeri 1987 and Te Puke 1989) to > 130 ml (Kerikeri 1988 proportion of this should be attributed to management practices such as fruit thinning. The fruit growth curves could be described by a two-phase curve, with a reduction in slope 50-60 days after flowering. The initial phase, up to 50 days from flowering, produced growth rates of 1.55 ml/day. The second, slower phase of growth, averaged 0.42 ml/day over the period to harvest. A simple linear regression model was used to predict the mean fruit volume at harvest from measurements of fruit volume made at a given time during the period from 50 to 110 days from flowering (typically mid January and mid March, respectively). The percentage of the variation in mean fruit volume at harvest accounted for by the regression was 75% when based on measurements made 50 days from flowering and rose to nearly 98%, 110 days from flowering. A similar approach was used to predict the standard deviation of fruit volume at harvest. The observed standard deviation at harvest varied from 10 ml to just over 20 ml, which is within the range published by others. The regression of the standard deviation of the fruit volume at harvest on the standard deviation of fruit volume earlier in the season accounted for more than 80% of the observed variation from 50 days after flowering onwards.

No abstract

Effects of hydrogen cyanamide (HC) application to kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A. R. Ferguson 'Hayward') vines were assessed over four seasons in three New Zealand kiwifruit-growing areas. HC advanced the date of budbreak to c. 40 days after application, despite the date of application varying from 33 to 92 days before natural budbreak. For every day that HC advanced budbreak, there was a 0.5-day advance in the date of flowering (r 2 = 0.92). The smaller advance in flowering resulted from the cooler temperatures experienced between budbreak and flowering in the treated vines. HC applications tended to reduce the spread of budbreak and flowering, with the greatest effect at the warmest sites. H01011 Received 19 March 2001; accepted 20 August 2001Application of HC usually increased budbreak and the total number of flowers at the warmest two sites, but only slightly reduced their seasonal variation as this was largely the result of the amount of winter chilling vines received. The number of flowers per winter bud produced by untreated vines was reduced by 0.44 per 1°C. The percentage of total flowers that were lateral or side flowers was reduced by HC application from 14 to 4% at the warmest site and 29 to 19% at the coolest site.