Bean seedling damage by root-feeding grubs (Schizonycha spp.) in Kenya as influenced by planting time,variety, and crop residue management

Use of legume cover crops to improve soil productivity has had unexpected effects on cropping system components in a maize (Zea mays L.) and bean (Phaseolus vulgaris L.) cropping system in Trans Nzoia district, Kenya. Smallholder farmers who recently adopted relay cropping of lablab (Lablab purpureus L.) observed a decline in bean yields where lablab residues had been incorporated prior to maize and bean planting. We investigated chafer grub (Schizonycha spp.) damage to beans and studied the impact of lablab and maize stover residue management strategy, planting time, and bean cultivar selection on seedling damage. Seedling assays (germination to flower initiation), involving four different bean varieties (GLP2, KK15, KK22, and KTL3), were carried out in three consecutive planting periods. The assays were superimposed on a long-term, factorial experiment where soils had been subjected to differential lablab and maize stover residue management strategies for 7 years. Factors were (1) lablab residues removed (L0) or retained (L1); (2) maize stover removed (S0) or retained (S1) and (3) residues left on the soil surface (I0) or incorporated (I1). Planting time significantly affected the degree of chafer grub damage, with later planted beans sustaining substantially more damage. Of the four bean varieties, KK15 and GLP2 were more grub tolerant than KK22 and KTL3. Grub damage was most severe in plots where lablab residues had been retained and maize stovers had been removed (L1S0). This factor combination had the highest seedling mortality, the poorest stand establishment, and the largest proportion of plants with severed roots systems. The results of this study show that the current farmer practice (lablab residue retention and maize stover removal) is conducive to increased grub-induced bean seedling damage and suggest that early planting, retention of maize stover, and selection of grub-tolerant varieties are important management strategies to reduce damage and subsequent productivity decline.     

Greenhouse gas emissions from a wastewater sludge-amended soil cultivated with wheat (Triticum spp. L.) as affected by different application rates of charcoal

Applying biochar to soil is an easy way to sequester carbon in soil, while it might reduce greenhouse gas (GHG) emissions and stimulate plant growth. The effect of charcoal application (0, 1.5, 3.0 and 4.5%) on GHG emission was studied in a wastewater sludge-amended arable soil (Typic Fragiudepts) cultivated with wheat (Triticum spp. L.) in a greenhouse. The application of charcoal at ≥1.5% reduced the CO₂ emission rate significantly ≥37% compared to unamended soil (135.3 g CO₂ ha⁻¹ day⁻¹) in the first two weeks, while the N₂O emission rate decreased 44% when 4.5% charcoal was added (0.72 g N₂O ha⁻¹ day⁻¹). The cumulative GHG emission over 45 days was 2% lower when 1.5% charcoal, 34% lower when 3.0% charcoal and 39% lower when 4.5% charcoal was applied to the sludge-amended soil cultivated with wheat. Wheat growth was inhibited in the charcoal-amended soil compared to the unamended soil, but not yields after 135 days. It was found that charcoal addition reduced the emissions of N₂O and CO₂, and the cumulative GHG emissions over 45 days, without altering wheat yield.     

Comparative Efficacy of White Mustard (Sinapis alba L.) and Soybean (Glycine max L. Merr.) Seed Meals as Bioherbicides in Organic Broccoli (Brassica oleracea Var. Botrytis) and Spinach (Spinacea oleracea) Production

White mustard and soybean seed meals were compared for weed control and yield of organically grown broccoli and spinach. The meals were incorporated into the soil 2 weeks before crop planting at two rates (1.24 and 4.48 t ha^?1). Weed densities and hand-weeding time were recorded twice during the growing seasons and weed biomass was measured at crop harvest. Compared to the 1.24 t ha^?1 soybean treatment, weed densities were 52 to 95% and 41 to 45% less at 3 and 6 weeks after planting, respectively, in both crops with the 4.48 t ha^?1 white mustard seed meal treatment. Time required for hand weeding at these times was also reduced by up to 82% and 48%, respectively. Broccoli yield was similar in all the treatments, but spinach yield was greatest in the 4.48 t ha^?1 treatments for both seed meals. Petiole nitrate and nutrient concentrations in both crops were generally similar in all the treatments.     

Genetic diversity and species delimitation in the cultivated and wild Guinea yams (Dioscorea spp.) from Southwest Ethiopia as determined by AFLP (amplified fragment length polymorphism) markers

Yams (Dioscorea spp.) rank as the fourth most important root and tuber crop after potatoes, cassava and sweet potatoes. They are an economic crop in most of the tropics especially in West Africa, which produces over 95 % of the world output. Despite their cultural and economic importance there is taxonomic confusion regarding Guinea yams. The currently used classification scheme, which relies on vegetative and inflorescence characters, does not consistently delimit species boundaries between members of Guinea yams (D. cayenensis Lam.–D. rotundata Poir. complex), their wild relatives (D. abyssinica Kunth and D. praehensilis Benth.,) and D. sagittifolia Pax. Establishing the taxonomic identity of the germplasm and understanding the systematic relationships among crops is vital to the management of genetic resources and the utilization of accessions. In this study, amplified fragment length polymorphism (AFLP) genetic fingerprinting was used to evaluate and characterize 43 individual plants, belonging to different populations of wild and cultivated Guinea yams. The three primer combinations used in the AFLP analyses generated 158 scorable bands, with an overall polymorphism of 78 %. Ordination and cluster analyses of AFLP data failed to produce any clear species boundary between either the Guinea yam accessions or between them and their wild relatives. The average genetic similarity between the study individuals of Guinea yams and their wild relatives ranged from 60 to 100 %. The first, second and third principal coordinates axes cumulatively account for 77.45 % of the total variation. AFLP analyses also revealed a higher genetic divergence among cultivated Guinea yam accessions of the Sheko cultivars. Ordination and cluster analysis using UPGMA revealed no clear species boundaries between members of the complex. Thus, the taxonomy of these “species” needs to be revisited using other markers.     

Isothiocyanate concentration in Kohlrabi (Brassica oleracea L. Var. gongylodes) plants as influenced by sulfur and nitrogen supply

Glucosinolates (GSss) represent bioactive compounds of Brassica vegetables whose health-promoting effects merely stem from their breakdown products, particularly the isothiocyanates (ITCs), released after hydrolysis of GSs by myrosinase. GSs are occasionally discussed as transient S reservoirs, but little is known concerning the interactive effect of S and N supply on ITC concentrations. Therefore, kohlrabi plants were grown in a pot experiment with varied S (0.00, 0.05, and 0.20 g pot (-1)) and N (1, 2, and 4 g pot (-1)) supplies. Plant growth exhibited a classical nutrient response curve with respect to both S and N. The ITC profile of kohlrabi tubers was dominated by methylthiobutyl ITC (11-1350 micromol (g DM) (-1)), followed by sulforaphan (7-120 micromol (g DM) (-1)), phenylethyl ITC (5-34 micromol (g DM) (-1)), and allyl ITC (5-38 micromol (g DM) (-1)), resulting from the hydrolysis of glucoerucin, glucoraphanin, gluconasturtiin, and sinigrin, respectively. The ITC profile was in agreement with reported data, and concentrations of all ITCs were substantially reduced in response to increasing N and decreasing S supply. A growth-induced dilution effect could be ruled out in most cases, and the results do not support the hypothesis that GS acts as transient reservoir with respect to S.     

Use of near-infrared spectroscopy for screening the individual and total glucosinolate contents in Indian mustard seed (Brassica juncea L. Czern. & Coss.)

The potential of near-infrared spectroscopy (NIRS) for screening the sinigrin, gluconapin, 4-hydroxyglucobrassicin, and total glucosinolate contents of Indian mustard (Brassica juncea L. Czern. & Coss.) seed was assessed. Intact seed samples of this species were analyzed by NIRS and their reference values regressed against different spectral transformations by modified partial least-squares (MPLS) regression. The coefficients of determination (r (2)) for sinigrin, gluconapin, 4-hydroxyglucobrassicin, and total glucosinolate contents were, respectively, 0.86, 0.95, 0.33, and 0.82. The standard deviation to standard error of prediction (SEP) ratio, and SEP to standard error of laboratory ratio were for these constituents as follows: sinigrin, 2.59 and 2.70; gluconapin, 4.16 and 2.08; 4-hydroxyglucobrassicin, 1.18 and 1.40; and total glucosinolates, 2.18 and 1.60. By comparison of commercial sinigrin spectrum with the first MPLS loadings of the sinigrin equation, it can be concluded that the molecule of sinigrin has a specific signal in the seed spectrum of Brassica.     

Glucosinolate concentration in turnip (Brassica rapa ssp. rapifera L.) roots as affected by nitrogen and sulfur supply

Three greenhouse pot experiments were conducted with four different nitrogen (N) treatments (80, 160, 240, and 320 kg ha (-1)) in combination with three sulfur (S) treatments (10, 20, and 60 kg ha (-1)) to study the effects of combined N and S supply on glucosinolate concentration and composition in turnip roots. Total glucosinolate concentration varied widely from 9.7 (N 320S 10) to 91.6 (N 160S 60) mg (100 g) (-1) root fresh weight (FW) and individual glucosinolate concentrations were increased with increasing S supply regardless of the N treatment, whereas enhanced N supply (160 - 320 N ha (-1)) at the high S level (60 kg ha (-1)) did not affect total glucosinolate concentration. In contrast, assumingly attributed to the individual glucosinolate biosynthesis concentration of N-containing tryptophan-derived indole glucosinolate was highest with increased N supply, whereas S-containing methionine-derived aromatic and aliphatic glucosinolates decreased with increasing N supply combined at low S level (10-20 kg ha (-1)).     

The domestication and dispersal of the cultivated ramie (Boehmeria nivea (L.) Gaud. in Freyc.) determined by nuclear SSR marker analysis

Ramie (Boehmeria nivea) was domesticated in China. However, the geographic region of domestication is not exactly known. Genetic diversity and population structure of ramie and their wild relatives were assessed using microsatellite markers. The 8 microsatellite primers revealed 96 alleles in 50 ramie populations, with an average of 10.25 alleles per locus. Cultivated ramie gene pool harbors approximately 82.9 % of the SSR diversity presented in wild B. nivea var. nivea. It is suggested that ramie has experienced a relatively moderate domestication bottleneck. The distribution of genetic diversity shows that genetic diversity is relatively high in populations along the Yangtze River compared to the peripheral ones. The scatter plots of principal coordinates analysis indicated that there are three well-supported varieties in B. nivea. The NJ tree and the distribution of genetic diversity showed that ramie has been domesticated in the middle and lower regions of the Yangtze valley, and populations in Sichuan province have been introduced from this region, forming naturalized populations.     

Quantification of zinc transport via the phloem to the grain in rice plants (Oryza sativa L.) at early grain-filling by a combination of mathematical modeling and 65Zn tracing

Zinc (Zn) is an essential nutrient for human beings, and most Zn intake occurs through vegetables or cereals such as rice (Oryza sativa L.) grains. Recently, we detected Zn as well as cadmium, which may be partitioned to rice grains, in the phloem saps from the uppermost internodes of rice and in the xylem saps from the cut stems at early grain-filling. To quantify Zn transport to the grains via the phloem and xylem, a mathematical model previously developed for cadmium transport to rice grains was applied. We examined the translocation of zinc into the grains of rice plants at early grain-filling by feeding zinc-65 (⁶⁵Zn) via a root-bathing medium, through culm cuts above and below the flag-leaf nodes, and through the flag leaves. The estimate made using the mathematical model and experimental data for three types of ⁶⁵Zn transport suggests that the grain Zn may be accumulated predominantly via the phloem through two means of transport, phloem transport of stored Zn from the leaves and, more importantly, xylem-to-phloem transfer at the nodes from Zn as it is being absorbed. The Zn transport via the phloem to the grains is more selective than that of cadmium, a non-nutrient element, as also evidenced by the greater transport of cadmium to the glumes via the xylem.     

Growth and iron nutrition of broccoli (Brassica oleracea L. var. italica Plenck), grown in a Typic Ustochrept, as influenced by vesicular-arbuscular mycorrhizal fungi in the presence of pyrite and farmyard manure

Greenhouse experiments were conducted using potted soil (Fe-deficient Typic Ustochrept) to study the influence of the vesicular-arbuscular mycorrhizal fungi (VAM), Glomus macrocarpum and G. fasciculatum, on the mobilisation of Fe in broccoli (Brassica oleracea L. var. italica Plenck) in the presence of pyrite and farmyard manure (FYM). Individual applications of either VAM or pyrite with NPK fertiliser significantly enhanced both the Fe²⁺ content in leaf tissue and total uptake of Fe and resulted in increased curd and straw yields of broccoli compared to those observed with NPK alone. Though the application of FYM decreased the Fe²⁺ content in leaf tissue relative to plants supplied NPK alone, this result was not statistically significant. The available Fe content in soil, after harvest of broccoli, was found to be lower in the presence of VAM than in the control. Received: 18 June 1997