Estimates of general combining ability in Hevea breeding at the Rubber Research Institute of Malaysia : I. Phases II and III A

Estimates of general combining ability of parents for yield and girth obtained separately from seedlings and their corresponding clonal families in Phases II and IIIA of the RRIM breeding programme are compared. A highly significant positive correlation (r = 0.71***) is found between GCA estimates from seedling and clonal families for yield in Phase IIIA, but not in Phase II (r = -0.03(NS)) nor for girth (r= -0.27(NS)) in Phase IIIA. The correlations for Phase II yield and Phase IIIA girth, however, improve when the GCA estimates based on small sample size or reversed rankings are excluded.When the best selections (based on present clonal and seedling information) are compared, all five of the parents top-ranking for yield are common in Phase IIIA but only two parents are common for yield and girth in Phases II and IIIA respectively. However, only one parent for yield in Phase II and two parents for girth in Phase IIIA would, if selected on clonal performance, have been omitted from the top ranking selections made by previous workers using seedling information.These findings, therefore, justify the choice of parents based on GCA estimates for yield obtained from seedling performance. Similar justification cannot be offered for girth, for which analysis is confounded by uninterpretable site and seasonal effects.

Heterogeneity of human whole blood platelet subpopulations. I. Relationship between buoyant density, cell volume, and ultrastructure

A quantitative high yield method utilizing isosmotic arabino-galactan (Stractan) solutions and isopycnic centrifugation was developed to isolate and to fractionate total human platelet populations into density-dependent subpopulations. Isolated platelets were free of factor VIII/von Willebrand factor and other plasma proteins. They responded to ADP, epinephrine, and collagen with a sensitivity equal to platelet-rich plasma platelets. The correlation of platelet density with volume and ultrastructure was examined for normal subjects. Recovery of total platelet populations averaged 92.76%+/-3.64% (SD). Normal individuals exhibited a narrow range of platelet buoyant density distribution. Computerized probability plot analysis of platelet volume distribution for 15 normal subjects' total platelet populations showed a mean volume of 5.17+/-0.46 cu mum (SD). Platelets with buoyant density less than or equal to 1.062 g/ml had a mean volume of 4.50+/-0.48 cu mum, while platelets with buoyant density greater than 1.071 g/ml, but less than or equal to 1.084 g/ml, had a mean volume of 5.32+/-0.63 cu mum (SD). The volume difference by paired t test was significant, p less than 0.001. Thin-section electron microscopy demonstrated a significant reduction of granule content in light platelets, as compared to heavy platelets, but an equal number of mitochondria for both groups. These differences of platelet volume and structure between light and heavy platelets suggested that aging may be a determinant of platelet heterogeneity.

Estimates of genetic parameters of certain characters in Hevea brasiliensis

Heritability estimates of five quantitative characters, namely, yield, girth, girth increment, virgin bark and renewed bark thickness, of the breeding Phase III Hevea families have been obtained by variance component analyses. In general, the combined heritability estimates for various characters were low to moderate. The heritabilities of these characters based on female variance components, however, were high, suggesting that considerable improvement of each of the characters could be achieved in properly designed experiments.Estimates of heritability for average yields (Range: 0.11-0.34) over different years showed that the first three years' yield was adequate for predicting estimates of genetic variance for the average of five years' yield.Correlation studies on yield with other characters indicated considerable influence of environment, with genetic correlations accounting for about 0.07 to 0.36 in the characters studied.Expected direct response to selection in yield and correlated response in yield to selection for girth at opening and virgin bark thickness have been calculated using three arbitrary values of selection intensity. The efficiency of the correlated response was found to be approximately half that of the direct response. However, the indirect selection for yield using virgin bark thickness appeared to be more favourable than that using the girth at opening favoured by earlier workers.

MUTATION SPECTRUM IN THE FUNGUS CONIOCHAETA VELUTINA

Auxotrophic, morphological, sensitive and suppressor mutant strains of Coniochaeta velutina are described. Of 1334 auxotrophic mutants isolated, all but 58 have been characterized as to their specific requirements. The mutation spectrum obtained on malt medium differs in several respects from that on complete medium. Arginine, adenine, cysteine, methionine, histidine and pyrimidine requiring mutants were most frequently isolated. Of 12 diauxotrophs tested genetically, 7 proved to be double mutants, but the remaining 5 behaved genetically as single mutants with a double requirement. Four of these required both adenine and histidine for growth and the other both phenylalanine and tyrosine. Cysteine-sensitive mutants and histidine-sensitive strains are described. Other mutants isolated included a variety of morphological, conidial and colour variants, UV-sensitive strains, canavanine-sensitive strains and arginine-suppressor mutations.

An introduction to the genetics of the fungus Coniochaeta veluitina

The fungus Coniochaeta velutina (Fuckel) Munk., which inhabits defective xylem in maple trees, has been developed for a joint genetical and plant pathological program. This paper describes progress made in the genetical aspect of the problem. From the more than 80 mutants forms which have been isolated after ultraviolet irradiation, 34 have been analyzed genetically by random spore analysis. Many of the mutant strains were incapable of acting as protoperithecial parents in crosses, thus limiting the number of crosses which could be made. Three linkage groups have been discovered, but many of the genes investigated showed no linkage with any other. This finding is in keeping with similar genetic analyses with other fungi.Linkage between the two pyrimidine-requiring mutants in Coniochaeta parallels a similar finding in Neurospora.