Establishment ability of cacao progenies in Nigeria

Summary Establishment of cacao farms in Nigeria is difficult mainly because of a severe dry season of three to four months.The results of three field trials designed to study and select progenies for good Establishment Ability are reported here. Good Establishment Ability was found in the wild Upper Amazon populations Nanay, Iquitos and Parinari, in Trinitario populations and the Scavina progeny.     

Establishment of cacao clones in nigeria

Summary The successful establishment of cacao (Theobroma cacao L.) farms in Nigeria is often difficult. The West African Amelonado cacao variety, planted in the Western Nigeria cacao-belt mainly during the 1930's can no longer be established in large, basically deforested areas. There is a great need for improved establishment methods and cacao varieties well adapted to exposed environmental conditions. The behaviour of 40 cacao clones under such conditions is reported. Clones originating from parents collected in 1938 from the Upper Amazon region in Peru have performed surprisingly well.     

Seasonal influences upon the pod weight of cacao and their consequences for selection

In a previous publication about the selection of cacao in West New Guinea, directions have been given on the production determination of individual trees. It was tacitly assumed that the pod weight of a given tree, although variable, would not change systematically with time. However, new data brought to light that this assumption was wrong. It was established that during the main harvest the average pod weight was considerably lower than during the remaining months. But as these changes of weight appeared to have no influence on the quotient pulp weight/pod weight, the method of production determination mentioned needs no revision.Present address: University of Science and Technology, Kumasi, Ghana.     

Inheritance of a weeping character and the low frequency of rooting from cuttings of the mulberry variety 'Shidareguwa'

A mulberry variety, Morus alba 'Shidareguwa', has a weeping habit and is used as an ornamental and landscape plant. This variety is known for being difficult to propagate by hardwood cuttings. To clarify the mode of inheritance of the weeping character and its relationship to the difficulty in cutting propagation, we crossed 'Shidareguwa' with a non-weeping variety 'Noi' that has a very high rooting ability. The phenotypic segregations exhibited by the F₁ and F₂ plants suggested that the weeping habit is controlled by a single recessive gene. In tests of the F₂ plants for cutting propagation, no obvious correlation was recognized between the weeping trait and the rooting ability of cuttings. As a result, we were able to develop new weeping mulberry strains with improved high rooting ability.     

Yield variation in the early productive years in trials with cacao (Theobroma cacao L.)

Summary Single tree yields of clones and hybrid seedlings in two cacao trials were analysed. During the first 3 years of production variability was high and frequency distributions were positively skewed. Apparently improved growing conditions in the fourth year resulted in a marked increase in mean yields and produced normal distributions and lower coefficients of variation. Clones and hybrids showed similar responses to annual effects. Early yields are not satisfactory for selection of individual phenotypes because of the nature of the distributions. In view of the tendency for variation to change with season it is suggested to base selection on the combination of several years' yields after the 8th year.     

Inheritance and general combining ability studies of detached pod, leaf disc and natural field resistance to Phytophthora palmivora and Phytophthora megakarya in cacao (Theobroma cacao L.)

Black pod is a major disease of cocoa. Knowledge of the inheritance of resistance to black pod would be important in devising strategies to breed resistant varieties. The mode of inheritance of resistance to black pod disease was investigated using leaf disc, detached pod tests and natural field observation in a 6?×?4 factorial and 6?×?6 diallel mating designs analyzed using North Carolina design-II approach and Griffing??s method II model I approach, respectively. The dominant component was smaller than the additive component for pod lesion size, leaf disc scores and natural field infection. Both general combining ability and specific combining ability (SCA) effects influenced the inheritance of pod lesion number and leaf disc scores suggesting that both additive and non-additive (dominance or epistatic) effects influence the inheritance of resistance to black pod disease. However, SCA effect was not significant for pod lesion size and natural field infection suggesting the importance of additive genes in the inheritance of these traits. The higher heritability of leaf disc scores, pod lesion numbers and pod lesion sizes than the heritability of natural field infection which was almost zero, shows the influence of environment on natural field infection and suggests that ranking of resistance of cocoa genotypes need to be done under controlled environmental conditions to observe true resistance levels. Good general combiners, in combination with each other, did not necessarily yield good specific combinations suggesting that parents?? performance cannot be used for selecting superior progenies. The non-significance of reciprocal effects indicates absence of maternal effects or cytoplasmic inheritance in resistance to black pod disease. Recurrent selection procedures and inter-crossing aimed at general combining ability would be more suitable for improvement of black pod disease resistance. Cocoa genotypes with good combining ability for resistance to black pod disease such as T60/887, Pa 150, Sca 6, and Pa7/808, identified in this study could be important parents to form base population for such recurrent selection procedures.     

Effect of meta-topolin on leaf senescence and rooting in Pelargonium × hortorum cuttings

Pelargonium (Pelargonium x hortorum) is grown as potted or bedding plants for their colourful, showy flowers and scented foliage. Absence of senescence symptoms in the leaves of Pelargonium cuttings, their capacity to initiate roots and continued growth of initiated roots is an important quality attribute. The effects of postharvest treatments with meta-topolin (mT) and thidiazuron (TDZ) to ‘Katinka’ Pelargonium cuttings were investigated. Leaves treated with mT or TDZ for 5 d had higher leaf chlorophyll contents than untreated controls. Exposing cuttings to mT had no effect on the rooting proportion (%) and average root diameter. Similarly, 0.05 mM mT had no effect on number of roots per cutting. However, mT slightly reduced root length, root surface area and total volume of the roots. TDZ severely inhibited adventitious root formation, thus it reduced all the root parameters investigated. In conclusion, mT is very active in retarding leaf senescence, and combined with the observed ease of rooting of cuttings after mT treatment, this treatment is a suitable alternative to TDZ in delaying the onset of leaf yellowing in ornamental crops.     

Repeatability and minimum harvest period of cacao (Theobroma cacao L.) in Southern Bahia

Classically, selection for superior genotypes in cacao has been based on the successive harvest records across a number of years. Little information on the minimum duration of these harvest periods is available in the literature. The repeatability coefficient (ρ) was used to estimate this period. Twenty five cacao genotypes were assayed in a randomized block design with four replications and 16-plant plots. The following yield components were studied: number of healthy fruits per plant, number of collected fruits per plant, weight of humid seeds per plant and per fruit, and percentage of diseased fruits per plant, over 5 years (1986–90). Repeatability estimates were higher than 0.84 for all components, except percentage of diseased fruits per plant (^ρ - 0.41). With such estimates, it is possible to select genotypes on the basis of only two years of successive harvests, with a determination coefficient of 90%. The advantages of applying the repeatability coefficient to the cacao breeding program are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation and utilisation of cacao (Theobroma cacao L.) germplasm at the International Cocoa Genebank, Trinidad

The aim of this study was to identify promising genotypes in the International Cocoa Gene bank, Trinidad (ICG,T) for use in cacao breeding. Subsets of the germ plasm collection were evaluated for bean number, bean weight, pod index (581 genotypes) and resistance to Phytophthora pod rot(500 genotypes). Among three groups of cacao assessed (For astero, Refractario and Trinitario), Trinitario had the highest percentage of genotypes (36.9%) with large bean weight (> 1.2 g), while For astero possessed the highest proportion of genotypes (22.6%) with a large number of beans (> 45). The ICS population had the highest percentage (44.1%) of genotypes with heavy beans, and IMC the highest percentage of genotypes with large bean number (68.6%). A low, but significant negative correlation (r = –0.19, p≤ 0.001) between bean number and bean weight suggests that an increase in bean number may repress an increase in bean weight and vice versa. However, inten genotypes good values of bean weight and number were combined demonstrating that selection for both large bean number and bean weight is possible. The highest percentage (28.1%) of genotypes with low pod index (< 20.1) was observed in the Trinitario group (mainly ICS). The Forastero group had the highest percentage of Phytophthora resistant accessions(18.0%). The PA population had the highest proportion of resistant (24.0%) and moderately resistant (38.0%)genotypes. Sixty-five and 99 genotypes were categorised with large bean weight and high bean number, respectively, and 60 genotypes were found with a low pod index. Seventy-eight genotypes were identified with resistance to Phytophthora podrot. A significant relationship was observed between resistance to Phytophthora pod rot (measured as the frequency of localised lesions) and bean number (r = –0.45, p ≤ 0.001)showing that the two traits may complement each other. The combination of low to intermediate pod index with moderate to high resistance to Phytophthora podrot was found in 87 genotypes, 12 of which were also reported to have resistance to witches’ broom disease. These genotypes are of high potential value in cacao breeding and their inclusion in working and corecollections would be justified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Parental genetic distance and combining ability analyses in relation to heterosis in various rice origins

Journal of Crop Science and Biotechnology - Information on parental genetic distance and combining ability is a fundamental prerequisite for hybrid rice breeding. Based on a study of genetic...     

Origin of haploids and semigamy in Theobroma cacao L.

Summary The origin of haploid plants of cacao was studied using morphological and enzyme markers. Analysis of 250 haploids arising either from controlled crosses or from open pollination in a biclonal seed-garden showed the existence of several types. They could be either or in origin, or chimaeric haploids or diploid/haploid chimaeras. In the majority of cases these chimaeras, visible at the cotyledon stage, were not maintained at the level of foliage, where only one genotype was observed. Studies of the haploid/diploid chimaeras show that the diploid part could be heterozygous and thus correspond to the fusion of the two parental gametes occurring after gametic cell divisions have produced haploid tissue. This phenomenon of semigamy could be facilitated in cacao by its particular system of self-incompatibility.     

提高植物试管苗生根率的技术与方法

组培快繁技术已广泛应用于"名、优、特、新、稀"植物品种的快速繁殖,其过程分为初代培养、继代增殖培养和试管苗生根及移栽.其中试管苗生根率高低关系到该技术能否在生产中应用.影响试管苗生根的因素很多,如试管苗本身生理生化状态,基本培养基,生长调节物质和外部因素等.作者经多年的科研实践和综合有关报道,认为提高试管苗的生根率应采用以下几种技术和方法.     

Heterosis in relation to genetic divergence and specific combining ability in groundnut (Arachis hypogaea L.)

Summary The frequency and magnitude of heterosis were examined in relation to genetic divergence among parents in two diallel cross experiments in groundnut. The parents were grouped into clusters based on their diver-gence. The range, mean and standard deviation of the intra-and inter-cluster divergence were used to define four divergence classes. The frequency of heterotic crosses and the magnitude of heterosis for yield and its components were found to be higher in crosses between the parents in intermediate divergence classes than extreme ones. The results agreed well with the overall status of the specific combining ability of these crosses.     

Genetic variation in dry weight of carnation cuttings: its causes and consequences

Summary Carnation cultivars vary considerably in the average weight of their cuttings. Cutting weight shows a high negative correlation with mean relative growth rate. This was initially attributed to differences in age of the cuttings when taken from the stock plants, age being defined as time elapsed since start of visible shoot growth. Shoots on a stock plant are removed as cuttings when they have reached an adequate size and number of leaf pairs. Cuttings from cultivars with a lower rate of growth are removed later, usually resulting in a higher dry weight. This could explain why a high cutting weight is associated with a low relative growth rate.The validity of this tentative explanation is tested in 13 carnation cultivars grown under controlled conditions in two trials, one with plants grown from pinched cuttings and one with plants grown from unpinched cuttings for early flowering (forcing). An analysis of the data for plant weight and leaf pair number at successive stages of development suggests that the primary cause of the negative correlation between cutting weight and mean relative growth rate is not genetic variation in age of the cuttings, but variation in the size of the fully developed axillary bud on the stock plant. Larger buds produce thicker shoots that grow more slowly. Their later harvesting as cuttings only enhances their initial weight advantage, and also the negative correlation with mean relative growth rate.When plants are pinched 20 days after planting, as is normal in a summer-grown crop, the newly developing shoots still show variation in age. This is attributed to variation in the developmental stage of the dormant axillary buds at the time of pinching, causing variation in the time interval between pinching and the start of visible shoot growth.     

Genetic divergence in parental genotypes and its relation with heterosis, F1 performance and general combining ability (GCA) in opium poppy (Papaver somniferum L.)

Summary Genetic divergence in 110 population (20 parents and 90 F₁ hybrids) of opium poppy was studied by multivariate analysis. All the entries were grouped in 14 clusters. Out of 20 parents, ten were accumulated in one cluster and rest 10 distributed over seven clusters. Estimates of cluster distance showed that maximum intra-cluster distance was in -cluster IX (25.62) followed by cluster I (22.41), V (22.23) and IV (21.06). The inter cluster distances varied from 16.62 (between cluster XII and XIV) to 195.10 (between cluster IV and IX). The cluster analysis indicated substantial diversity among the parental genotypes, which had the potential to release considerable variation in their crosses. The first four principal components (PCs) with eigen values >1 accounted for 68% of variation among the population. The first and second components could account for 29 and 20% of the total morphological and alkaloidal variations, respectively. The PC1 was closely related to yield and yield related traits. The characters contributing greatest positive weight on PC1 were opium yield, plant height, stem diameter, capsule weight/plant and seed yield/plant. The possibilities of relationship between genetic divergence, F₁ performance, heterosis and GCA of parents have been explored.