Lack Of Winter Chilling Research Articles

Chilling Requirements of Apricot (Prunus armeniaca L.) Cultivars Using Male Meiosis as a Dormancy Biomarker.

Apricot has undergone an important cultivar renewal during the last years in response to productive and commercial changes in the crop. The impact of the sharka disease (plum pox virus) prompted the release of cultivars resistant/tolerant to this virus, leading to a major cultivar renewal worldwide. This has caused high variability in chilling requirements on new releases that remain unknown in many cases. In many apricot-growing areas, the lack of winter chilling is becoming a limiting factor in recent years. To deal with this situation, growers must choose cultivars well adapted to their areas. However, the information available on the agroclimatic requirements of the cultivars is very limited. To fill this gap, in this work, we have characterized the chilling requirements of 13 new apricot cultivars from Europe (France, Greece and Spain) and North America (USA) in two experimental collections in Aragón (Spain). We established the chilling period using male meiosis as a biomarker for endodormancy release over two years. Chilling requirements ranged from 51.9 Chill Portions (CP) to 70.9 CP. Knowing the chilling requirements of cultivars will help growers to select suitable cultivars adapted to the chill availability of their region.

Oklahoma Deciduous Trees Differ in Chilling Enhancement of Budburst

In many tree species, winter chilling accelerates budburst in response to spring warmth. Global climate change has already accelerated budburst in deciduous tree species around the world. But as global climate change leads to milder winters, tree species also experience less chilling, which may actually delay spring budburst in some species. We hypothesized that reduced duration of winter chilling would delay spring budburst in sycamore ( Platanus occidentalis ) and pecan ( Carya illinoinensis ), but would not delay it in sweetgum ( Liquidambar styraciflua ). We tested this hypothesis experimentally by manipulating the number of weeks of chilling from 0 to 6 weeks. Lack of winter chilling did not delay budburst in sweetgum but did delay it in sycamore and pecan, in agreement with the hypothesis. Mild winters in Oklahoma may eventually favor the growth of sweetgums at the expense of sycamores and pecans.

Abnormal Anther and Pollen Development in Sweet Cherry Cultivars Resulting from Lack of Winter Chilling

Lack of pollen dispersal was noted in various sites and cultivars of sweet cherry (Prunus avium) following one of California's warmest recorded winters (≈550 hours @ 7°C in the Central Valley). `Bing' cherry is thought to require 850 to 880 hours for adequate budbreak and bloom development. Cross pollination is required by most sweet cherry cultivars for fruit set, including `Bing'. Complete anther dehiscence averaged 13% in `Bing' trees sampled, compared to 52% in `Rainier', 65% in `Brooks', 84.5% in `Burlat', 33% in Van, 23% in `Larian', and 86% in `Black Tartarian'. A range of degree of dehiscence from none to half-open was widely apparent, again by cultivar. Many partially dehiscent anthers did not shed pollen normally but appeared to have the mass of pollen completely adherent inside the pollen sacs. `Black Tartarian', `Larian', and `Burlat' shed pollen readily, however, pollen from dehiscent anthers of other cultivars generally appeared to stick together on the everted locule walls and required direct manipulation to be withdrawn from the pollen sac. Anther morphology ranged from normal size to half normal size, anthers appearing to be without pollen altogether that shriveled on drying, and lobes that were aborted. Pollen germination was low overall: 19% `Bing', 18% `Rainier', 20% `Brooks', 57% `Burlat', 14% `Van', 48% `Larian', and 48% `Black Tartarian'. Poor fruit set in low chill years is often attributed to lack of bloom overlap with pollenizers, however, inadequate chilling also may contribute to low fruit set by inhibiting anther and pollen growth and development. The implications of a critical chilling requirement for normal floral differentiation are that in cherry-growing areas where low chill years are common, pollen may not be viable or transferrable from pollenizers and female gametophytic development also may be impaired.

EFFECT OF HYDROGEN CYANAMIDE (DORMEX) SPRAYS ON PEACH TREES SUFFERING FROM LACK OF WINTER CHILLING.

Lack of winter chilling (480 hrs. at or below 7.2°C by 02/28/89) occurred along Alabama's Gulf Coast in the winter of 1988-89. Varieties requiring 650 hours of chilling or more were under stress. To evaluate hydrogen cyanamide (HC), a product used world wide to replace part of some fruit plants chilling req., a study was conducted along the Gulf Coast using Bicentennial (700 hr.), Sentinel (850 hr.) and Loring (900 hr.) peach varieties. Full tree sprays (applied to drip with handgun) using 0, .5 and 1% a.i. plus .25% × 77 were applied 03/01/89. Fruit buds were dormant to slight swell when sprayed. HC greatly enhanced rate and % of leaf bud break at the 1% conc., for all varieties. Rate and % of flowering were significantly increased at 1% conc. in Loring and Sentinel but nearly all fruit dropped. Flowering, yield and fruit size of Bicentennial-were significantly improved at .5 and 1% conc. HC was effective in replacing lack of chilling in this variety.

Growth regulation in top fruit

Growth regulators offer possibilities of compensating for genotypic deficiencies that, in top fruit, would take many years to alter by genetical methods and, in marginal climates, they can help to overcome environmental shortcomings such as spring frosts or lack of winter chilling. In addition to their use in the control of growth and fruiting, they have made possible the development of advanced experimental systems in which pruning and harvesting may be fully mechanized.