Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. ex Fr. I. Fertility in F1 hybrids and backcrosses to C. Arabica

Summary The interspecific (C. arabica × tetraploid C. canephora) F₁ hybrid showed a low but highly variable fertility. An almost complete restoration to normal fertility was observed in individual trees of BC₁ and BC₂ generations with C. arabica as recurrent parent. From a comparison of various tests of fertility, it was found that pollen viability is a satisfactory measure of fertility.     

Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. Ex Fr. II. Meiosis in F1 hybrids and back crosses to C. Arabica

Summary Melosis was studied in Coffea arabica, in induced tetraploid C. canephora, in their F₁ hybrid (arabusta hybrid) and in backcross generations of the hybrid with C. arabica as recurrent parent. Irregularities were observed, consisting of univalents (especially in the arabusta hybrid), multivalents (especially in tetraploid C. canephora) and uneven distribution of chromosomes at first anaphase. Chromosome distribution was improved by backcrossing. Meiotic irregularities wer negatively correlated with pollen fertility.     

Antinociceptive and antiplasmodial activities of cassane furanoditerpenes from Caesalpinia volkensii H. root bark

The chloroform and ethyl acetate extract (100 mg/kg) of Caesalpinia volkensii H. exhibited significant (P ≤ 0.05) antinociceptive activities using hot plate and writhing tests in mice while the later showed antiplasmodial activity (IC₅₀ 0.23 ± 0.07 and 4.39 ± 2.49 μg/ml) against chloroquine sensitive (D6) and chloroquine-resistant (W2), respectively. Two new furanoditerpenes [rel. 1β,5α-dihydroxyvoucapane (1) and rel. 1β,6β-dihydroxyvoucapane; 19β-methyl ester (2)] together with seven known compounds [voucapane (3), voucapan-5-ol (4), deoxycaesaldekarin C (5), caesaldekarin C (6), 5-hydroxyvinhaticoic acid (7), triacontanyl-(E)-ferulate (8), triacontanyl-(E)-caffaete (9) and 30′-hydroxytriacontanyl-(E)-ferulate (10)] were isolated from the two extracts. The administration of 3, 4, 5 and 6 (100 mg/kg i.p) caused a significant (P ≤ 0.05) reduction in the number of writhing episodes induced by acetic acid and (P ≤ 0.01) increased pain latency threshold in hot-plate test compared to control. However, the pure compounds indicated relatively (P ≤ 0.05) low antiplasmodial activity. The phytochemical constituents from the root bark of C. volkensii had better analgesic properties than antimalarial properties, justifying the use of the plant root bark as a remedy for pain.     

Comparison of the sensitivity of the mean and the mode in screening coffee seedlings for resistance to coffee berry disease Colletotrichum coffeanum Noack sensu Hindorf (A short communication)

Summary The utility of the modal grade as an alternative to the mean grade in the pre-selection test for screening seedlings of Coffea arabica L. for resistance to coffee berry disease (CBD) caused by Colletotrichum coffeanum NOACK sensu HINDORF was examined. Three criteria were used to compare the sensitivity of the modal grade with that of the mean grade when partitioning 6 weeks old seedlings into different resistance classes. The criteria were: the sensitivity of the two statistics as estimators of central tendency, the sensitivity of the modal grade and the mean grade as selection criteria and the correlation between the two statistics.The modal grade was neither more sensitive in detecting genotypes that fell in diffent resistance classes nor more severe than the mean grade in screening for genotypes susceptible to CBD. In the cases studied, the modal grad was highly correlated with the mean grade (r_s ranged from 0.55^**–0.82^**). Hence, it is concluded that there are practically no gains in adopting the modal grade as a pre-selection criterion in preference to the mean grade.     

Productivity and nitrogen use of tea plantations in relation to age and genotype

Lack of science-based knowledge on responses of tea bushes to nitrogen (N) in ageing tea plantations hampers the development of ecologically sound and economically profitable N-management strategies. It is hypothesized that ageing of tea plantations lowers productivity and weakens the yield response to N application. To establish insight into the relationship between ageing, productivity and N-use efficiency, seasonal and annual responses to N were studied in field experiments superimposed on a chronosequence of tea plantations (14, 29, 43, and 76 years). The two youngest plantations comprised of a clonal cultivar planted at a density of 10,766 and 13,448 plants ha⁻¹ and the two oldest plantations of seedlings at a density of 6730 and 7179 plants ha⁻¹, respectively. N was applied as urea at 0, 50, 100, 200, and 400 kg N ha⁻¹ year⁻¹.Mean annual made tea (mt) yields were higher for the clonal tea compared to the seedling tea and increased with age within genotypes. The clonal bushes out-yielded the seedlings by about 800 kg mt ha⁻¹ under favourable weather conditions in 2003/2004, while yield differences between the genotypes were minimal under stress conditions in 2002/2003. The yields of the clonal 29- and 14-year-old plantations responded positively to N fertilizer, whereas the 43- and 76-year-old plantations did not. Within the clonal cultivar made tea yield and N uptake were closely associated. Apparent shoot N-recovery (ASNR) based on N uptake by ‘two leaves and a bud’ was higher in clonal than in seedling tea plantations. A simple N-balance sheet showed that N excess was strongly associated with the rate of N application and N uptake.The effect of plant genotype on productivity was greater than the effect of age. The genotypes (seedlings or a clonal cultivar) to a great extent determined the yield response to N. In a well-managed mature tea plantation of up to 80 years, ageing did not lower the yielding ability within the same genotype. Thus, planting improved genotypes and implementing appropriate N-management strategies are key factors to avoid the risk on decline of productivity and profitability associated with ageing and bush degradation. N-management strategies should be based on the yielding potential of tea bushes in the target environment as defined by plant genotype and age of plantations.     

Microscale ecological stress causes RAPD molecular selection in wild barley, Neve Yaar microsite, Israel

Genetic micro-differentiation was studied in wild barley at the Neve Yaar microsite, Israel, an area of 3182 m², which includes a mosaic of sun-rock, sun-soil, shade-rock, and shade-soil microniches. Fifty-six genotypes were tested for ecological-genetic microniche correlates. Analysis of 75 RAPD loci revealed a significantly higher polymorphism and gene diversity (P _0.05 = 0.920; He = 0.411) on the more stressful sun-rock microniche, compared to the least stressful shade-soil microniche (P _0.05 = 0.653; He = 0.188). Fifty-six (74.7%) out of the 75 loci varied significantly in allele frequencies. On the average, of the 75 loci, 75.7% of the total genetic diversity exists within the four microniches, while 24.3% exists between the microniches. The highest genetic distance was between shade-soil and sun-rock (D = 0.220), which confirmed their sharp microecological contrasts. Gametic phase disequilibria (LD) differed significantly between sunny and shady microniches. The levels of correct classification of individual genotypes into their respective microniche, based on the presence/absence of bands of the 2, 3, 4, 5, and 7 best differentiating loci, obtained by stepwise discriminant analysis, were 79, 84, 89, 95, and 100%, respectively. We conclude that ecological contrasts at the Neve Yaar microsite cause molecular diversifying selection (presumably at both coding and noncoding genomic regions of wild barley) overriding gene flow.     

A seedling inoculation test for screening Sesbania sesban for resistance to the seedling defoliator, Mesoplatys ochroptera

The seedling beetle Mesoplatys chroptera is a serious pest of Sesbania sesban and other Sesbania spp. that are important agroforestry species. Sesbania sesban was compared to Sesbania micrantha, Sesbania goetzi and Sesbania cinerascens, in a seedling inoculation test for resistance to Mesoplatys ochroptera using copulating adult instars as inoculum. The uniform susceptibility of Sesbania sesban including accessions from western Kenya was confirmed. But S. cinerascenswas found to be resistant to the pest. This revised version was published online in June 2006 with corrections to the Cover Date.     

Contents Volume 118, 2001

Volume Contents

Contents Volume 118, 2001     

Direct seeding of Sesbania sesban for green manure in agroforestry systems — a short communication

This study was based at the Agroforestry Research Centre, Maseno Kenya. The objective was to evaluate the effects of pre-treatment, seed rate and depth of sowing seed on direct seeding of Sesbania sesban. Direct seeding was shown to be feasible during the rainy season, provided a shallow seed bed was used. Direct seeding at 3 cm furrow depth led to significantly (P = 0.05) greater germination compared to 10 cm depth. There was no effect of pretreatment and seed rate on germination, early seedling growth and dry matter partitioning. Depth of sowing similarly had no effect on early growth and dry matter partitioning. Establishment by direct seeding is relatively non-labour intensive with a probable high adoption potential.This revised version was published online in November 2005 with corrections to the Cover Date.