Yield,Potassium Uptake,and Use Efficiency in Upland Rice Genotypes

Potassium (K) is an essential nutrient for higher plants. Information on K uptake and use efficiency of upland rice under Brazilian conditions is limited. A greenhouse experiment was conducted with the objective to evaluate influence of K on yield, K uptake, and use efficiency of six upland rice genotypes grown on Brazilian Oxisol. The K rate used was zero (natural soil level) and 200 mg K kg^–1 of soil. Shoot dry weight and grain yield were significantly influenced by K level and genotype treatments. However, K × genotype interactions were not significant, indicating similar responses of genotypes at two K levels for shoot dry weight and grain yield. Genotypes produced grain yield in the order of BRS Primavera > BRA 01596 > BRSMG Curinga > BRS 032033 > BRS Bonança > BRA 02582. Potassium concentration in shoot was about sixfold greater compared to grain, across two K levels and six genotypes. However, K utilization efficiency ratio (KUER) (mg shoot or grain yield / mg K uptake in shoot or root) was about 6.5 times greater in grain compared to shoot, across two K level and six genotypes. Potassium uptake in shoot and grain and KUER were significantly and positively associated with grain yield. Soil calcium (Ca), K, base saturation, acidity saturation, Ca saturation, K saturation, Ca/K ratio, and magnesium (Mg)/K ratio were significantly influenced by K application rate.     

EVALUATING POTASSIUM-USE-EFFICIENT COTTON GENOTYPES USING DIFFERENT RANKING METHODS

Identification of cotton (Gossypium hirsutum L.) genotypes efficient in potassium (K) uptake and utilization, under K-deficient conditions represents a cost-effective and environmentally friendly approach for low-K-input agriculture. It would reduce the costly input of K-fertilizers and manage K resources in agro-ecosystems. We ranked 25 cotton genotypes for their K use efficiency under deficient and adequate K regimes in hydroponics, using two different methods. K deficiency generally reduced cotton growth; however, K-efficient genotypes accumulated more biomass due to higher K uptake. Genotype NIBGE-2 exhibited excellent adaptation potential in terms of high shoot dry weight under both K regimes and ranked as the only most desirable, “efficient-responsive” genotype. Genotype CIM-506 produced low shoot dry weight under low K condition and ranked as “non-efficient.” Genotype Desi okra produced low shoot dry weight at adequate K level and ranked as “non-responsive.” Genotype ranking using two different methods ensured the validity of results.     

Differences in shoot growth and zinc concentration of 164 bread wheat genotypes in a zinc‐deficient calcareous soil

Abstract

A greenhouse experiment was carried out to study severity of the zinc (Zn) deficiency symptoms on leaves, shoot dry weight and shoot content and concentration of Zn in 164 winter type bread wheat genotypes (Triticunt aestivum L.) grown in a Zn‐deficient calcareous soil with (+Zn=10 mg Zn kg^?1 soil) and without (‐Zn) Zn supply for 45 days. Tolerance of the genotypes to Zn deficiency was ranked based on the relative shoot growth (Zn efficiency ratio), calculated as the ratio of the shoot dry weight produced under Zn deficiency to that produced under adequate Zn supply. There was a substantial difference in genotypic tolerance to Zn deficiency. Among the 164 genotypes, 108 genotypes had severe visible symptoms of Zn deficiency (whitish‐brown necrotic patches) on leaves, while in 25 genotypes Zn deficiency symptoms were slight or absent, and the remaining genotypes (e.g., 31 genotypes) showed mild deficiency symptoms. Generally, the genotypes with higher tolerance to Zn deficiency originated from Balkan countries and Turkey, while genotypes originating from the breeding programs in the Great Plains of the United States were mostly sensitive to Zn deficiency. Among the 164 wheat genotypes, Zn efficiency ratio varied from 0.33 to 0.77. The differences in tolerance to Zn deficiency were totally independent of shoot Zn concentrations, but showed a close relationship to the total amount (content) of Zn per shoot. The absolute shoot growth of the genotypes under Zn deficiency corresponded very well with the differences in tolerance to Zn deficiency. Under adequate Zn supply, the 10 most Zn‐ inefficient genotypes and the 10 most Zn‐efficient genotypes were very similar in their shoot dry weight. However, under Zn deficiency, shoot dry weight of the Zn‐efficient genotypes was, on average, 1.6‐fold higher compared to the Zn‐inefficient genotypes. The results of this study show large, exploitable genotypic variation for tolerance to Zn deficiency in bread wheat. Based on this data, total amount of Zn per shoot, absolute shoot growth under Zn deficiency, and relative shoot growth can be used as reliable plant parameters for assessing genotypic variation in tolerance to Zn deficiency in bread wheat.     

GENOTYPIC DIFFERENCES IN PHOSPHORUS UPTAKE AND UTILIZATION OF WATERMELON UNDER LOW PHOSPHORUS STRESS

In this study, seven watermelon (Citrullus lanatus) cultivars were tested in solution culture experiment with limiting and ample phosphorus (P) supply to evaluate P uptake and utilization of watermelon under low P stress. Different genotypes showed considerable diversity in terms of biomass accumulation, P uptake, P utilization, root morphological parameters and photosynthetic parameters under low P stress. At low P supply, genotype XN8 and ZCHY were clearly superior to other genotypes in terms of total dry matter yield. The genotype ZJ has the highest P uptake ability, while the genotype XN8 has the highest P efficiency ratio and P utilization efficiency among the seven genotypes under low P stress. The P uptake ability of these genotypes was related significantly and positively to root morphological parameters and photosynthesis parameters under low P stress, the P utilization efficiency showed significant and positive correlation with total dry matter. Results showed existence of genetic differences among watermelon genotypes with regard to P absorption and utilization. The seven genotypes were classified into four groups: efficient responsive (ER), inefficient responsive (IER), efficient non-responsive (ENR) and inefficient nonresponsive (IENR) according to P utilization efficiency under low P stress and dry matter at high P supply. XN8 was identified as ER, and ZCHY was identified as ENR, which may be valuable resources for watermelon production in different soil with low P stress.     

Genotypic variation of potassium uptake and use efficiency in cotton (Gossypium hirsutum)

Potassium (K) deficiency is one of the main limiting factors in cotton (Gossypium hirsutum L.) production. To study the mechanism of high K‐use efficiency of cotton, a pot experiment was conducted. The experiment consisted of two cotton genotypes differing in K‐use efficiency (H103 and L122) and two K‐application levels (K₀: 0 g (kg soil)^–1; K₁: 0.40 g (kg soil)^–1). Root‐hair density and length, partitioning of biomass and K in various organs, as well as K‐use efficiency of the two cotton genotypes were examined. The results show that there was no significant difference in K uptake between the two genotypes at both treatments, although the genotype H103 (high K‐use efficiency) exhibited markedly higher root‐hair density than genotype L122 in the K₁ treatment. Correlation analysis indicates that neither root‐hair density nor root‐hair length was correlated with plant K uptake. Furthermore, the boll biomass of genotype H103 was significantly higher than that of genotype L122 in both treatments, and the K accumulation in bolls of genotype H103 was 39%–48% higher than that of genotype L122. On the other hand, the litter index (LI) and the litter K‐partitioning index (LKPI) of genotype H103 were 14%–21% and 22%–27% lower than that of genotype L122. Lastly, the K‐use efficiency of total plant (KUE‐P) of genotype H103 was comparable with that of genotype L122 in both treatments, but the K‐use efficiency in boll yield (KUE‐B) of genotype H103 was 24% and 41% higher than that of genotype L122 in K₀ and K₁ treatments. Pearson correlation analysis indicated that KUE‐P was positively correlated with BKPI and negatively correlated with LKPI, while KUE‐B was positively correlated with BKPI and boll‐harvest index (HI_B), and negatively correlated with LKPI. It is concluded that there were no pronounced effects of root‐hair traits on plant K uptake of the two genotypes. The difference in K‐use efficiency was attributed to different patterns of biomass and K partitioning rather than difference in K uptake of the two genotypes.     

Genotypic Variation of Sweetpotatoes Grown Under Low Potassium Stress

Abstract

Ninety‐four sweetpotato (Ipomoea batatas L.) genotypes were compared under low potassium (K) stress (35 mg kg^?1 dry soil) over two growing seasons. Potassium utilization efficiency ratio (KER), defined as the dry matter weight/K content, was significantly different among genotypes. Genotypes were divisible into four KER categories: high efficient, efficient, fairly efficient and inefficient with most of the genotypes falling in the efficient and fairly efficient groups. The K contents varied significantly within individual plants. Potassium concentration on a dry weight basis was greatest in the petioles followed by leaves, stems, and roots. On a total plant basis, K content in roots was greatest followed by stems, leaves, and petioles. Several genotypes (including 602 × 81‐3, Zhe15‐47 and Xushu18) were selected as most suitable for growth on soils low in available K due to their appreciable yields and higher KER under low K stress.     

Nitrogen‐use efficiency traits of mini‐watermelon in response to grafting and nitrogen‐fertilization doses

Two experiments were conducted to study the effect of grafting on nitrogen‐use efficiency (NUE) in mini‐watermelon plants. In the first study, mini‐watermelon plants (Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa) either ungrafted or grafted onto Macis, Vita (Lagenaria siceraria [Mol.] Standl.), PS1313, and RP15 (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root‐to‐shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity 40 d after transplantation in response to nitrate concentration in the nutrient solution (0.5, 2.5, 5, 10, 15, or 20 mM of NO$ _3^- $ ). In the second experiment, the suitability of a selected rootstock with high NUE (Vita) to improve crop performance and NUE of grafted mini‐watermelon plants was evaluated under field conditions. In the hydroponic experiment mini‐watermelon grafted onto Vita rootstock needed the lowest nitrate concentration (1.31 mM of NO₃) in the nutrient solution to reach half maximum shoot dry weight. Total leaf area, SPAD index, and shoot N uptake increased in response to an increase of N concentration in the nutrient solution. At 2.5 mM NO$ _3^- $ , mini‐watermelon grafted on either Vita or RP15 had the highest NR activity whereas no significant difference was observed at 10 mM NO$ _3^- $ . The open‐field study indicated that increasing N‐fertilization rates from 0 to 100 kg ha^–1 improved total and marketable yields of mini‐watermelon plants while decreasing NUE. When averaged over N levels, the marketable yield, NUE, N‐uptake efficiency, and N‐utilization efficiency were significantly higher by 39%, 38%, 21%, and 17%, respectively, in Minirossa grafted onto Vita compared to ungrafted Minirossa plants. Therefore, grafting mini‐watermelon plants onto selected rootstocks can be used as a quick and effective method for improving productivity and NUE.     

Potassium Substitution by Sodium in Root Medium Influencing Growth Behavior and Potassium Efficiency in Cotton Genotypes

ABSTRACT

Potassium (K) deficiency affects cotton (Gossypium hirsutum L.) growth. Sodium (Na) can substitute K for some non-specific functions in plants. Four cotton genotypes were evaluated for their growth rates and K use efficiency grown at various K:Na. The cotton genotypes and treatments had significant (p < 0.01) effect on biomass production, growth rate related parameters, K use efficiency, and K: Na ratio. Maximum total dry matter (2.57 g plant^-1) was accumulated by ‘NIBGE-2’ and minimum (1.91 g plant^?1) was by ‘FH-1000’. Maximum K:Na ratio in shoot was obtained by ‘MNH-786’ and minimum was by ‘NIBGE-2’when 1/3rd K was replaced with Na. Genotypes and various treatments significantly (p < 0.05) influenced specific utilization rate (SUR) and K transport rate (KTR). There was a significant relationship (R² = 0.84, n = 60) between shoot dry matter and K: Na ratio in shoot. Overall, the growth was better when K and Na were added in ratio of 3:1.     

Phosphorus‐use efficiency by corn genotypes

Phosphorus (P) deficiency is a principal yield‐limiting factor for annual crop production in acid soils of temperate as well as tropical regions. The objective of this study was to screen nine corn (Zea mays L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of P applied in an Oxisol. Plant height, root length, shoot dry weight, root dry weight, shoot‐root ratio, P concentration in shoot and root, P uptake in root and shoot, and P‐use efficiency parameters were significantly (P<0.01) influenced by P treatments. Significant genotype differences were found in plant height, shoot and root dry weight, P uptake in root and shoot, and P‐use efficiency. Based on dry matter production and P‐use efficiency, genotypes were classified as efficient and responsive, efficient and nonresponsive, nonefficient and responsive, and nonefficient and nonresponsive.     

Nitrogen Use Efficiency in Cacao Genotypes

Cacao (Theobroma cacao L) is mostly grown on soils with low natural fertility. On such soils nitrogen (N) is one of the most yield limiting nutrients for cacao. Information is lacking on N use efficiency in cacao. A greenhouse experiment was conducted to evaluate growth response and N use efficiency by two cacao genotypes. The genotypes used were TSH-565 and ICS-9 and N rates adapted were 0, 120, 240, 360, and 480 mg N /pot. In both genotypes, increasing levels of applied N improved growth (stem girth, dry weight of shoot and roots and shoot/root ratio), and concentration and uptake of N. Genotypes differed significantly for stem girth and ICS -9 produced greater stem girth compared with TSH-565. Nitrogen uptake had a linear relationship with root dry weight of the two genotypes. In both genotypes, increasing levels of applied N overall increased N-uptake efficiency (NEFF = N concentration in shoot x shoot/root), but decreased N-use efficiency by shoot and roots (NUE = g dry matter of shoot or root/mg N) and N-use efficiency of carbohydrate (NUEC = mg of total carbohydrates in shoot/mg of N in shoot). Both genotypes responded differently to applied N, despite the existence of close genetic relatedness between them. The method used here appears to be suitable method for identification of cacao genotypes that are efficient in uptake and utilization of N.     

Upland rice genotypes evaluation for phosphorus use efficiency

Phosphorus (P) deficiency is one of the most important yield‐limiting factors in acid soils in various parts of the world. The objective of this study was to evaluate the growth and P‐use efficiency of 20 upland rice (Oryza sativa L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of applied P on an Oxisol. Plant height, tillers, shoot and root dry weight, shoot‐root ratio, P concentration in root and shoot, P uptake in root and shoot, and P‐use efficiency were significantly (P<0.01) affected by level of soil P as well as genotype. Shoot weight and P uptake in shoot were found to be the plant parameters most sensitive to P deficiency, suggesting that these two parameters may be most suitable for screening rice genotypes for P‐use efficiency under greenhouse conditions.     

Potassium-Use Efficiency in Upland Rice Genotypes

Potassium (K) uptake is greatest among essential nutrients for rice. Data related to yield, yield components, and K-use efficiency by upland rice genotypes are limited. A greenhouse experiment was conducted to evaluate influence of K on growth, yield and yield components, and K-use efficiency by upland rice genotypes. Potassium levels applied to an Oxisol were zero (natural K level) and 200 mg K kg¹ of soil and 20 upland rice genotypes were evaluated. Plant height, shoot dry weight, grain yield, 1000-grain weight, and spikelet sterility were significantly affected by K and genotype treatments. Genotypes Primavera and BRA 1600 were the most efficient and genotype BRAMG Curinga was most inefficient in producing grain yield. Plant growth (plant height and shoot dry weight) and yield components (panicle number, grain harvest index, 1000-grain weight, and panicle length) were significantly and positively associated with grain yield. However, spikelet sterility was significantly and negatively correlated with grain yield.     

低钾胁迫下水稻钾高效基因型若干生长特性和营养特性的研究

采用溶液培养筛选,结合田间试验,提出了采用低钾胁迫下水稻体内钾利用效率作为衡量水稻钾利用效率的指标;探讨了钾高效基因型水稻的若干生长特性和营养特性;指出低钾胁迫导致水稻生物量减少,植株生长缓慢,分蘖能力差,根系生长受到抑制,根系吸收的钠增加。水稻钾高效基因型低钾胁迫下仍具有较强的生长势(相对干重、相对株高、相对根长较大),其地上部钾/钠比值高而根部钾/钠比值较低,地上部和根部钾/氮吸收量比值较低。     

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P‐efficient genotypes. Two efficient and two inefficient genotypes were investigated for P‐efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P‐uptake rate of roots but decreased root‐to‐shoot ratio, root‐hair length, and P‐utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot–dry matter yield and relative shoot‐growth rate at low P supply, and therefore can be considered as P‐efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P‐utilization efficiency and that of CIP 384321.3 to both higher P‐uptake efficiency in terms of root‐to‐shoot ratio and intermediate P‐utilization efficiency. Phosphorus‐efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P‐utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P‐utilization efficiency. Simulation of P uptake revealed that no other P‐mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.     

Evaluation of common bean genotypes for phosphorus use efficiency

A greenhouse experiment was conducted to evaluate phosphorus (P)‐use efficiency of 10 promising genotypes of common bean (Phaseoius vulgaris L.) with short and normal growth duration. The genotypes were grown on an Oxisol at 25 mg P kg^‐1 (low P) and 150 mg P kg^‐1 (high P) of soil. Shoot and root dry weight, root length, P concentration in the shoot, and P uptake in the shoot were significantly (P<0.01) affected by soil P concentration and genotype. However, P level did not effect root length and genotype had no effect on root dry weight. On the basis of P‐use efficiency (mg dry weight of shoot/mg P accumulated in the shoot) genotypes were classified as efficient and responsive (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NER), and nonefficient and nonresponsive (NENR). From a practical point of view, genotypes which produce a lot of dry matter in a soil with a low P level, and respond well to added P are the most desirable because they are able to express their high yield potential in a wide range of P environments. Novo Jalo and Pérola genotypes fall into this group. Genotypes Irai, Jalo Precoce and L93300166 fall into the ENR group. Genotypes Carioca, Rosinha G‐2, and Xamengo were classified NER, whereas, genotypes L93300176 and Diamante Negro were classified as NENR. There were no differences between short and normal growth duration genotypes in P‐use efficiency.     

K高效和K低效基因型水稻Na和K的吸收和分布与水稻生长及体内K利用率之间的关系

A pot experiment with two rice (Oriza sativa L.) genotypes differing in internal potassium use efficiency (IKUE) was conducted under different sodium (Na) and potassium (K) levels. Adding NaCl at a proper level enhanced rice vegetative growth and increased grain yield and IKUE under low potassium. Addition of higher rate of NaCl had a negative effect on the growth of the K-efficient rice genotype, but did not for the K-inefficient genotype. Under low-K stress, higher NaCl decreased IKUE of the K-efficient rice genotype but increased IKUE for the K-inefficient genotype. At tillering stage and under low-K stress, adding NaCl increased K and Na contents and decreased the ratio of K/Na for both genotypes. At harvesting stage under low-K stress, adding NaCl increased K and Na contents and K/Na ratio for the K-efficient genotype but decreased the K/Na ratio for the K-inefficient genotype. The accumulated Na was mostly deposited in the roots and sheaths. At tillering stage, the K and Na contents and the K/Na ratios in different parts for both genotypes decreased in the following sequence: K⁺ in sheaths > K⁺ in blades > K⁺ in roots; Na⁺ in roots > Na⁺ in sheaths > Na⁺ in blades; and K/Na in sheaths >> K/Na in roots. The K-efficient genotype had a lower K/Na ratio in roots and sheaths than the K-inefficient genotype under low-K stress. At harvesting stage, K and Na contents in grains were not affected, whereas K/Na ratio in the rice straws was increased for the K-efficient genotype but decreased for the K-inefficient genotype by Na addition. However, this was not the case under K sufficient condition.     

Improving potassium acquisition and utilisation by crop plants

To avoid loss of yield, crops must maintain tissue potassium (K) concentrations above 5–40 mg K (g DM)^–1. The supply of K from the soil is often insufficient to meet this demand and, in many agricultural systems, K fertilisers are applied to crops. However, K fertilisers are expensive. There is interest, therefore, in reducing applications of K fertilisers either by improving agronomy or developing crop genotypes that use K fertilisers more efficiently. Agronomic K fertiliser use efficiency is determined by the ability of roots to acquire K from the soil, which is referred to as K uptake efficiency (KUpE), and the ability of a plant to utilise the K acquired to produce yield, which is referred to as K utilisation efficiency (KUtE). There is considerable genetic variation between and within crop species in both KUpE and KUtE, and chromosomal loci affecting these characteristics have been identified in Arabidopsis thaliana and several crop species. Plant traits that increase KUpE include (1) exudation of organic compounds that release more non‐exchangeable soil K, (2) high root K uptake capacity, (3) early root vigour, high root‐to‐shoot ratios, and high root length densities, (4) proliferation of roots throughout the soil volume, and (5) high transpiration rates. Plant traits that increase KUtE include (1) effective K redistribution within the plant, (2) tolerance of low tissue K concentrations, and, at low tissue K concentrations, (3) maintenance of optimal K concentrations in metabolically active cellular compartments, (4) replacement of K in its non‐specific roles, (5) redistribution of K from senescent to younger tissues, (6) maintenance of water relations, photosynthesis and canopy cover, and (7) a high harvest index. The development of crop genotypes with these traits will enable K fertiliser applications to be reduced.     

Salt‐resistant and salt‐sensitive wheat genotypes show similar biochemical reaction at protein level in the first phase of salt stress

Salinity has a two‐phase effect on plant growth, an osmotic effect due to salts in the outside solution and ion toxicity in a second phase due to salt build‐up in transpiring leaves. To elucidate salt‐resistance mechanisms in the first phase of salt stress, we studied the biochemical reaction of salt‐resistant and salt‐sensitive wheat (Triticum aestivum L.) genotypes at protein level after 10 d exposure to 125 mM–NaCl salinity (first phase of salt stress) and the variation of salt resistance among the genotypes after 30 d exposure to 125 mM–NaCl salinity (second phase of salt stress) in solution culture experiments in a growth chamber. The three genotypes differed significantly in absolute and relative shoot and root dry weights after 30 d exposure to NaCl salinity. SARC‐1 produced the maximum and 7‐Cerros the minimum shoot dry weights under salinity relative to control. A highly significant negative correlation (r² = –0.99) was observed between salt resistance (% shoot dry weight under salinity relative to control) and shoot Na⁺ concentration of the wheat genotypes studied. However, the salt‐resistant and salt‐sensitive genotypes showed a similar biochemical reaction at the level of proteins after 10 d exposure to 125 mM NaCl. In both genotypes, the expression of more than 50% proteins was changed, but the difference between the genotypes in various categories of protein change (up‐regulated, down‐regulated, disappeared, and new‐appeared) was only 1%–8%. It is concluded that the initial biochemical reaction to salinity at protein level in wheat is an unspecific response and not a specific adaptation to salinity.     

Growth,water use efficiency,and sodium and potassium acquisition by tomato cultivars grown under salt stress

Three cultivars of tomato (Lycopersicon esculentum Mill., cvs. Sera, 898, Rohaba) were grown under different levels of NaCl in nutrient solution to determine effects of salt stress on shoot and root dry matter (DM), plant height, water use efficiency (WUE, g DM kg^‐1 water evapotranspired), shoot sodium (Na) and potassium (K) concentrations, and K versus Na selectivity (S_K,Na). Increasing NaCl concentration in nutrient solution adversely affected shoot and root DM, plant height, WUE, K concentration, and K/Na ratio of all cultivars. Shoot Na concentrations increased with increasing NaCl concentration in the nutrient solution. Although increasing salt concentration in the solution adversely affected growth of all cultivars, the cultivar Sera had the highest shoot and root DM than the other two cultivars (898 and Rohaba). Shoot and root DM of cultivar 898 was most affected by salt, while cultivar Rohaba had an intermediate salt sensitivity. The cultivar Sera generally had higher WUE values, shoot K concentrations, and S_K,Na, but had lower shoot Na concentrations than the other two cultivars when plants were grown under different salt levels. Greater Na exclusion, higher K uptake and shoot S_K,Na are suggested as being plant strategies for salt tolerance.     

Polymorphisms Among Chloroplast and Mitochondrial Genomes of <Emphasis Type="Italic">Citrullus</Emphasis> Species and Subspecies

Twelve and six DNA clones representing various parts of chloroplast and mitochondrial genomes, respectively, were used to detect polymorphism among five watermelon cultivars and 21 U.S. Plant Introductions (PIs) collected from diverse geographical locations and representing major groups of Citrullus species. Cluster analysis based on 20 chloroplast DNA (cpDNA) and 10 mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) markers differentiated the accessions into three major phenetic groups: PIs and watermelon cultivars of Citrullus lanatus subsp. vulgaris (Schrad. ex Eckl. et Zeyh.) Fursa (also designated as C. lanatus var. lanatus) (group I), PIs of C. lanatus var. citroides (of C. lanatus subsp. lanatus Schrad. ex Eckl. et Zeyh.)(group II), and C. colocynthis (L.) Schrad. PIs (group III). The chloroplast and mitochondrial genomes of watermelon cultivars are distinct, but closely related to those of the C. lanatus var. lanatus PIs. On the other hand, the chloroplast and mitochondrial genomes of the wild species C. colocynthis are more similar to those of C. lanatus var. citroides. Polymorphic cpDNA and mtDNA markers identified in this study can complement isozyme and nuclear DNA data used in earlier phylogenetic and phenetic classifications of Citrullus PIs. These cpDNA and mtDNA markers are being used in experiments designed to enhance watermelon cultivars by replacing the chloroplast and mitochondrial genome of cultivated watermelon with those of the wild species C. colocynthis.