The measurement and interpretation of genotype-environment interactions

Summary The regression analysis developed by Finlay and Wilkinson to investigate genotype-environment interactions and to assess genotypes for their adaptation to a range of environments is reviewed. Their analysis used the mean yield of many genotypes to provide a measure of the environment; it was not measured in physical terms. To reveal aspects of their analysis it was applied to data of the response of genotypes to variation in a single precisely measured environmental factor. The conclusions were extended to consider variation in several environmental factors.The effects on the regression statistics that occur with different samples of genotypes, sub- and super-optimal environmental conditions, differences in periods of growth, changes in the scale of measurement and the occurrence of several stress factors are outlined.The study byBreese (1969) of genotype-environment interaction inDactylis glomerata is considered against a background of these effects.     

Promotion of pistillate flowering inCucurbita by 2-chloroethylphosphonic acid

Summary All accessions tested of four cultivated species ofCucurbita responded to seedling treatment with 250 ppm 2-chloroethylphosphonic acid by developing only pistillate flowers for an extended period. This growth regulator is a promising means of facilitating hybrid seed production of squash. A similar treatment did not induce flowering of wild species ofCucurbita that were vegetative under the environmental conditions of the experiment.Approved by the Director of the New York State Agricultural Experiment Station for publication as Journal Paper No. 1737.     

Peridermium pini (Pers.) Lev. and the Resin-top Disease of Scots Pine: II. Lesion Anatomy

The stages in the formation of Peridermium pini lesions aredescribed. The hyphae of the parasite were septate, uninucleate,and intercellular, with unbranched haustoria penetrating allphloem cells and xylem parenchyma cells. Lesion extension occurredby apical growth of the hyphae along the outer edge of the functionalphloem. The hyphae stretched unbroken across the active cambium.Active centripetal and longitudinal growth of the mycelium occurredin the resin ducts of the xylem, the hyphae commonly reachingthe pith. Spermogonia were produced in late summer and fall,aecia appeared in spring. In lesion xylem, tracheids were shorter,rays taller, more numerous and wider, but ray cell height remainedunchanged. Fusiform rays increased in number and size and verticalresin ducts increased in number. Changes in xylem tissues didnot become evident until two to four years after invasion ofthe cambium by the mycelium. Invasion of the secondary phloemresulted in an increase in number and size of the longitudinalphloem parenchmya cells, while changes in phloem rays were similarto those in xylem rays.     

The application of ultraviolet microscopy to the distribution of lignin in wood description and validity of the technique

A method has been developed for the determination of lignin distribution in the wood cell wall by ultraviolet microscopy. The method incorporates some important advances on previus applications of UV microscopy to the study of lignin distribution. Ultrathin cross-sections of wood are obtained by the sample preparation and sectioning techniques of electron microscopy. The specimens are examined in monochromatic ultraviolet light using quartz reflection optics. The microscope image is photographically recorded and the negative is subsequently subjected to densitometric analysis. Each stage of the analytical procedure has been critically assessed to determine its validity and limitations. The method is ideally suited to the study of the removal of lignin from the wood cell wall during cooking and possesses other important applications in wood technology.     

THE USE OF LIVEWEIGHT-GAIN TRIALS FOR PASTURE EVALUATION IN THE TROPICS

An experiment is described in which liveweight gains were measured from two grass/legume pastures using small East African Zebu animals and also progeny of small East African Zebu cows crossed with Bos taurus bulls. Significantly higher production was obtained from cross-bred stock, which averaged 706 lb liveweight gain at per annum (791 kg/ha per annum), compared with 509 lb liveweight gain/ac per annum (571 kg/ha per annum) from Zebu stock, indicating that pasture management had advanced beyond the genetic potential of the local Zebu stock. The problems of designing, conducting and interpreting the results of such grazing trials are discussed.     

THE USE OF SHEEP FITTED WITH OBSOPHAGEAL FISTULAE IN GRAZING STUDIES

Studies were carried out on the effects of diurnal variation, fasting before sampling, and acclimatization to a sward on the chemical composition and in vitro OM digestibility of samples of extrusa collected from sheep fitted with oesophageal fistulae. The N content of extrusa samples increased markedly during the morning, and tended to decline again in the evening. The diurnal changes in digestibility were similar, but the variation was much smaller. There was no significant correlation between either N content or OM digestibility and grazing speed measured in bites per minute. There were no significant changes in either the N content or OM digestibility of successive samples of extrusa collected after over-night fasting, or after the sheep were introduced to a sward to which they were not accustomed, though the concentration of ash in the extrusa was significantly lower when the sheep were hungry than when they were not. The OM digestibility of the diet selected was approximately two units lower on the first two days after introduction to a new sward than the mean value of samples collected over the next 12 days.