Search Results
Abstract
For the first decades of the twentieth century, as with the last decades of the nineteenth, men were limited in attempts at crop improvement to manipulating the environment in which the plant grew or to changing the plant, through breeding, to better fit its environment. Great strides were made in increasing productivity by determining and optimizing fertility levels, water regimes, genetic composition of plants, and by protecting desirable plants and plant parts from insects, diseases, rodents and other pests. We began this era with crop plants which, under “ideal conditions”, could harvest a small percentage of the sun’s energy striking their leaf surfaces. After several decades we still find ourselves in the position of depending on greater leaf surfaces in a relatively protected and engineered environment to attain high yields. While we probably should not “knock” that which has worked so well in the past, the specter of widespread hunger, malnutrition, growing populations and possible competition for some segments of the food supply for energy production indicates additional gains in plant productivity will be beneficial, if not absolutely necessary.
Abstract
Abnormal development of the calyx end of ‘Golden Delicious’ apples (Malus domestica Borkh.) results in roundish-oblate fruit with rudimentary calyx lobes in a flattened basin. Persistent symptoms were caused by holding fruits at −1 to −2°C for 15 min, 21 days after full bloom or by dipping fruit in aqueous NaF solutions. Dipping fruit in 2,4-dichlorophenoxyacetic acid (2,4-D) or fumigating with HF produced typical foliage symptoms but did not affect fruit development.
Abstract
The effects of light intensity and leaf temperature on the net photosynthetic rate of rapidly growing ‘Golden Delicious’ apple (Malus domestica Borkh.) shoots were determined in a temperature range (-1.6 to 44°C) broader than previously reported. Under saturating light conditions the rate of CO2 uptake increased with leaf temperature to 2.7 g CO2 m2hr-1 at 25°. Optimum temperature decreased as the light intensity decreased, indicating a relationship between temperature and light saturation levels. At 25 to 30° the light saturation point was equivalent to 86 W/m2 of incident electromagnetic energy at wavelengths of 400 to 750 nm. At temperatures higher than the optimum, the rate of carbon dioxide uptake decreased rapidly. At 47 to 50° and high light intensities, the rate of carbon dioxide uptake was 0.3 to 0.5 g CO2 m-2hr-l.
Abstract
A system for monitoring CO2 flux in deciduous fruit trees was developed that allows simultaneous, independent control of climatic variables over a wide range. For such a system to work effectively, attention must be given to proper sealing of the chamber, placement of components within the system and disturbances which may arise from the functioning of control and sampling loops. Using the system described, it was found that the occurrence of a light frost after ‘Golden Delicious’ apple trees (Malus domestica Borkh.) had begun to produce vegetative growth drastically affected the carbon flux within the plant. These changes took place even though the cold stress was not severe enough to cause any discernible visual symptoms. Subsequent exposure of the trees to favorable growing conditions after a light frost resulted in the gradual recovery of the photosynthetic rate to levels approaching but not equal to that occurring in tissues of unstressed trees.
Abstract
Three levels of irrigation, dry, normal, and wet regimes, with and without 0.9 kg of supplemental nitrogen were applied during late spring to bearing pear (Pyrus communis L.) cv. ‘Beurre ‘d’Anjou’ trees commencing in 1979. In each of the 3 years tested, the percentage of trees affected with alfalfa greening and cork spot was greatest for the high level of irrigation. In 1979, alfalfa greening was associated with the high levels of leaf nitrogen and with the trees receiving supplemental nitrogen in the wet block. Fruits harvested from the wet block in 1979 were larger and firmer than fruit from the dry block, but the latter were higher in soluble solids.
Abstract
Although upper limitations on photosynthesis by apple trees are imposed by the structure and biochemistry of the leaf, an apple tree has a considerable potential for the fixation of carbon. Within these limits it is important to determine factors that prevent attainment of the tree’s full biological productivity. This review describes our present knowledge of some of these factors, both environmental and internal, that determine the actual biological productivity of the apple tree.
Abstract
A pear anthesis phenology model was used to determine timing of placement of reflector boards near ‘Seckel’ pear trees, or polyethylene hotcaps over them to accelerate their bloom for optimum pollination of ‘Anjou’. The normal full bloom date of ‘Anjou’ was predicted from the Utah chill unit (CU) and growing degree hour (GDH) models. ‘Bartlett’ pear phenology and historical bloom divergence of ‘Seckel’ and ‘Anjou’ were used in the absence of ‘Seckel’ and ‘Anjou’ phenology to determine the timing and amount of supplemental thermal accumulation. Bloom-accelerating techniques were placed on the pollinizer trees at an intermediate anthesis stage. Polyethylene hotcaps accelerated bloom effectively.
Abstract
Limbs of ‘Miller Sturdeespur Delicious’ apple trees (Malus domestica Borkh.) with bearing spurs ranging in age from 2 to 11 years were provided with differing solar exposure levels ranging from 5% to 95% of full sunlight (400 to 700 nm) from 55 days postbloom until harvest. As the exposure level of the limb canopy was reduced, fruit length, width, weight, soluble solids, starch content, and total solids were reduced while fruit firmness and total acidity were increased. Visual fruit red color of this high-coloring strain was not affected. As spur age increased, fruit length, width, weight, and soluble solids decreased while fruit firmness and total acidity increased. Spur age did not influence fruit red color, starch content, or total solids. Light exposure level accounted for a relatively large portion of the variation in fruit size and quality between limbs while spur age accounted for only a small portion of the variation within each limb.