Plant polyphenols have gained prominence in quality of plant products and in human health. An experiment was conducted to determine the association of tea polyphenols with water stress and their suitability as indicators for drought tolerance. The experiment was conducted in a 'rain-out' shelter, and consisted of six tea clones (BBK 35, TRFK 6/8, TRFK 76/1, TRFK 395/2, TRFK 31/30, and TRFK 311/287) and four levels of soil water contents (38, 30, 22, and 14% v/v), which were maintained for a period of 12 weeks. The treatments were arranged in a completely randomized design and replicated three times. Plant growth was monitored over 6 weeks, and a water stress index was calculated to determine water-stress tolerant clones. Total polyphenols in tea shoots was analyzed and a regression analysis done. The results indicate that declining soil water content (SWC) reduced both growth and content of polyphenols in tea. Tolerant clones maintained a high polyphenol content at low SWC, and also showed less fluctuation in phenolics when subjected to changes in SWC. There was significant (P < 0:001) correlation of total polyphenol content with shoot growth and WSI of tea, and a linear relationship (r 2 ¼ 0:97) between SWC for tea and both, water stress index and shoot polyphenol content. We report that there is a potential to use polyphenols as indicators for selection of droughttolerant tea cultivars.Key words: tea (Camellia sinensis L.); polyphenols; soil water content; drought tolerance Tea (Camellia sinensis L.) is rich in polyphenol compounds which have been a subject of study as to their effects on human health. [1][2][3][4][5][6][7][8] The crop is the source of manufactured tea, which is consumed worldwide but its production is constrained by frequent recurrence of drought in major production areas.9-11) Tea germplasm that can tolerate low soil water content (SWC) can reduce the losses occasioned by drought in production areas. Readily identifiable indicators for drought tolerance would hasten development and selection of tea germplasm for water stress environments. Plant response to stress is often manifested by its physiological and biochemical reactions, which can provide a basis for screening and selection of individual varieties and germplasm resistant to stress factors. For instance, plants are known to accumulate organic osmolytes, such as proline, glycine betaine, non-reducing sugars, and polyols 12,13) in response to stress factors. Though these organic compounds are species specific, their role is not clearly defined, but it is generally accepted that they contribute to ameliorating stress in plants. [13][14][15] Most of the stress-related organic compounds are secondary plant metabolites and incidentally, tea contains large amounts of polyphenols, particularly of the flavonol class. Some polyphenol derivatives have been used in quality determination in black tea 16) and in fruits, 17) but the role of polyphenols in drought stress and their suitability as indicators of desiccation tolerance in tea have not be...

2 A study to determine the association of fertilizer with soil water deficit in tea [Camellia sinensis (L.) O. Kuntze] was conducted in a rain-out shelter using potted plants, in which five rates of fertilizer (0, 75, 150, 225 and 300 kg Nitrogen ha −1 ) and six levels of soil water content (38, 34, 30, 26, 22 and 18% v/v) were applied in a complete randomized design and replicated three times. The soil water treatment was maintained for a period of 12 weeks during which shoot growth, plant water relations, and dry matter partitioning in tea were determined. A parallel field experiment with the above fertilizer rates was conducted at three sites in which shoot density and shoot weight were determined during the dry season. Fertilizer improved leaf-to-root and leaf-to-total mass ratios (P < 0.001), reduced shoot growth, shoot water potential and specific leaf area (P < 0.001). The fertilizer exacerbated drought effect on tea through disproportionate assimilate partitioning which consequently weakened the ability of tea to tolerate water stress. Results suggest an indirect contribution of fertilizer supply to drought susceptibility in tea.

Striga [Striga hermonthica (Del.) Benth.] is a parasitic angiosperm that infects tropical cereals causing severe yield losses. This study was conducted to determine if Striga damage in maize (Zea mays L.) can be mediated by the amount, form, and timing of N availability; and if the efficacy of N is contingent upon its regulation of assimilate partitioning. Two experiments were conducted in Kibos, western Kenya, in 1989 and 1990 on fields that had uniform Striga infestation. One experiment evaluated N rates of 0, 30, 60, and 90 kg N ha−1 supplied as either urea, calcium ammonium nitrate, ammonium sulfate, or ammonium sulfate plus the nitrification inhibitor dicyandiamide, while a second experiment evaluated similar N rates applied at 14, 21, 28, and 35 d after planting. Although Striga infection generally declined with increasing N availability, the impact was partially dependent on the severity of infestation as all N rates decreased infection in 1990, while only 90 kg N ha−1 reduced infection in 1989. Under high parasite densities in 1989, only urea reduced Striga (26%), while in 1990, infection was significantly decreased (an average of 30%) by all sources of N. In both years, N application at 28 d after planting resulted in the least Striga infection. Although assimilate partitioning during vegetative growth was unresponsive to N treatments, N availability during reproductive growth altered dry matter partitioning in favor of the ear over the vegetation. Averaged across N rates, this alteration resulted in increases in grain yield (64%) and harvest index (27%), and a decrease in source‐sink partitioning (41%) and in the concentration of nonstructural carbohydrates in the stalk (16%). Based on these data, N fertility can mediate the impact of Striga infestation on maize by altering assimilate partitioning in favor of the ear.

High fertiliser costs and declining soil fertility are'among the key factors contributing to low crop yields in Kenya. The contribution of five legumes grown in the short-rains season to soil nitrogen status and performance of a succeeding maize (Zea mays L.) was studied in an experiment at Njoro and Rongai within the Rift Valley Highlands of Kenya, from 1997 to 1999. Treatments included a weedy fallow, five grain legumes and maize (H513) grown during short-rains season followed by maize in the April-August long-rains season. The legumes were chickpea (Cicer arietinum L.), field bean (Phaseolus vulgaris L.), soybean [Glycine max(L.) Merril], garden pea (Pisum sativum L.), dolichos [Lablab purpureus (L.) Sweet]. The crop residues and vegetation of the weedy fallow were incorporated in the soil during seedbed preparation for the long rains season. The maize test crop was supplied with three levels of nitrogen, 0,30, and 60 kg ha-' as main factor whilst fallow management options were allocated as sub-factors in a split-plot treatment arrangement of a randomised complete block design replicated three times. Results show improved soil N status following legumes, with dolichos giving highest available N. Grain yield in maize succeeding legumes was 2468% higher than maize succeeding weed fallow. In the absence of N fertiliser input, maize succeeding dolichos gave 20-40% higher yield than maize after weed fallow treated with recommended 60 kg N ha-' fertiliser rate. The study has demonstrated that the use of grain legumes, particularly dolichos in rotation with maize, is a viable and preferable option to weedy fallows and maize-maize sequences.

An experiment was conducted to determine the association of tea catechins to water stress in tea, with the objective of determining their suitability as indicators for predicting drought tolerance in tea (Camellia sinensis). The study consisted of six tea clones (BBK 35, TRFK 6/8, TRFK 76/1, TRFK 395/2, TRFK 31/30, and TRFK 311/287) and four levels of soil water content (38, 30, 22, and 14% v/v), which were arranged in a complete randomized design and replicated 3 times. The treatments were maintained for a period of 12 weeks. Tea shoots were sampled for catechin analysis during the 6th week of water treatment, in which fresh shoots with two leaves and a bud were plucked and steamed for 2 min, and dried at 70 C to constant weight. Subsequently, the samples were ground and analyzed for catechins using an HPLC system. The total catechins showed significant correlation with shoot growth (r ¼ 0:65, P ¼ 0:006), soil water content (r ¼ 0:54, P ¼ 0:0066), and water stress index (r ¼ 0:67, P ¼ 0:0004). The epicatechin (EC) correlated with shoot growth (r ¼ 0:58, P ¼ 0:0032), soil water content (r ¼ 0:62, P ¼ 0:0014), and water stress index (r ¼ 0:63, P ¼ 0:0010). Similarly, epigallocatechin (EGC) correlated with shoot growth (r ¼ 0:65, P ¼ 0:0006), soil water content (r ¼ 0:50, P ¼ 0:0133), and water stress index (r ¼ 0:60, P ¼ 0:0021). However, epigallocatechin gallate (EGCg) and epicatechin gallate (ECG) showed no significant response to changes in soil water content. The shoot contents of EC and EGC in the six clones showed varied responses, with a distinct pattern in the water-stress tolerant clones (TRFK 6/8 and TRFK 31/30). The results suggest a potential use for EC and EGC as indicators in predicting drought tolerance in tea.Key words: catechins; drought stress; flavan-3-ol; free radicals Plants are known to accumulate organic osmolytes such as proline, glycine betaine, non-reducing sugars, and polyols 1,2) in response to stress factors. Though these organic compounds are species-specific their role is not clearly defined, but it is generally accepted that they contribute to ameliorating stress in plants. [2][3][4] Most stress-related organic compounds are secondary plant metabolites, and tea (Camellia sinensis) contains large amounts of polyphenols, mainly catechins, that belong to the flavan-3-ol class. Flavonoids play a key role in quality determination in black tea, 5) and in fruits, 6) but their role as indicators of desiccation tolerance in tea has not been explored. The precursors of most flavonoids are malonyl-CoA, derived from carbohydrate metabolism and p-coumaroyl-CoA, from the phenylpropanoid pathway. 7-9) Phenylpropanoids, which include flavonoids, isoflavonoids, and stilbenes, are derived from deamination of phenylalanine by phenylalanine ammonialyase (PAL). Flavonoid biosynthesis is dependent on structural and regulatory genes; structural genes encode enzymes catalyzing the biosynthesis, while regulatory genes control the expression of the genes. 8,[10][11][12][13][14] This implies that the availab...