A Review of Some Non-Destructive Linear Measurement Procedures for Leaf Area Determination in Crops

In the determination of leaf area, predictive regression models derived from linear measurements have been shown to correlate very well with actual leaf area. These predictive regression models are crop specific. Several reports, however, have shown that the use of linear measurements have been very much abused as models determined for one crop, for instance, has been severally been used for others. Thus, this paper reviews linear measurement procedures and predictive equations for some commonly researched crops. Leaf area determined from linear measurements is based on the area of a given surface being a product of length and width. From the model: length x width x 0.75 first reported for maize, models have been developed, in cucumber for instance, to include a single measurement of length in order to reduce the amount of time used in carrying out measurements. Int. J. Agric. Rural Dev., 2003, 4: 74-8

Molecular marker analysis of F1 progenies and their parents for carotenoids inheritance in African cassava (Manihot esculenta Crantz)

Cassava genotypes were assessed at genomic DNA level to estimate the genetic diversity within and between them using 36 simple sequence repeat markers (SSR). One hundred and forty-seven (147) F1 progenies derived from crosses amongst the parental genotypes were used to determine the association between three SSR markers and beta-carotene content in cassava. For the diversity study, a total of 131 alleles with an average of 3.7 alleles per locus were found. One yellow fleshed root genotype clustered with a white fleshed root genotype indicating similarity in their genetic background. Three SSR markers were used to screen the parental genotypes and their 147 progenies for a beta-carotene gene. The yellow fleshed root parents and 141 of the F1 progenies had SSR alleles associated with the presence of beta-carotene gene. The SSR markers identified for beta carotene at CIAT appeared linked to the trait as found in the parents, but evaluation in the progenies indicated that each marker did not account for high phenotypic variance individually. Marker NS 717 (allele 206) accounted for 20% beta carotene content and SSRY 301 (allele 331) accounted for 17%. There are minor QTLs that could probably be involved in beta carotene expression. The markers evaluated therefore do not sufficiently account for beta-carotene expression in the F1 progenies.Keywords: Cassava, simple sequence repeat (SSR), pro-vitamin A, diversity, validation. African Journal of Biotechnology, Vol 13(40) 3999-400

Growth, Yield And Disease Responses Of 12 Cassava Genotypes Evaluated For Two Cropping Seasons In A Derived Savannah Zone Of South-Eastern Nigeria

Ten new cassava genotypes selected for high yield and tolerance to some biotic stresses were evaluated alongside the local best, Otupam and ‘TMS 30572\' (a widely cultivated hybrid genotype, as an improved check) for two cropping seasons with a view to obtaining suitable genotype(s) that could be recommended for release to farmers. The results revealed that only TMS-96/0304, TMS-96/1672 and NR-930255 had above 90% sprout survival at 12 months after planting. Severity of cassava mosaic disease (CMD), cassava anthracnose disease (CAD) and cassava bacterial blight (CBB) varied among genotypes, plant age, and the cropping year. Symptom expressions of CMD and CBB were generally higher on the local best, Otupam and NR-930255. The severity of cassava green mite was moderate and statistically similar on all the genotypes while severity of cassava mealybug was mild. Hybrids NR930255, TMS96/1672 and TMS96/0304 produced the highest number of tubers. These genotypes also significantly (P< 0.05) produced the highest harvested tuber yield per hectare: NR 930255 (31.0 t/ha), TMS 96/1672 (28.0 t/ha) and TMS 96/0304 (29.4 t/ha). The three genotypes had the least percent yield difference between the potential and the actual yield. Mean rank-sum for all traits measured suggested that the most adaptable genotypes to Nsukka agro-ecology after two years of evaluation were NR-930255, TMS 96/0304 and TMS96/1672, but the poor disease ratings for NR-930255 and TMS 96/0304 precluded their recommendation for release while TMS 96/1672 could be recommended for release to farmers.Agro-Science Vol. 7 (2) 2008: pp. 162-16

Promiscuous arbuscular mycorrhizal symbiosis of yam (Dioscorea spp.), a key staple crop in West Africa

Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical "tree-aspect" savannas and dry forests that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18-25 vs. 11-16 spp.), but similar for both ecosystems (29-36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70-95 vs. 11-20%). After 8 months of trap culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems prevailing in West Africa