Salt-tolerance in Brassica juncea L. I. In vitro selection,agronomic evaluation and genetic stability

Summary In vitro selection of salt tolerant plants of Brassica juncea L. (Indian mustard) cv. Prakash has been accomplished by screening highly morphogenic cotyledon explant cultures on high NaCl media. Out of a total of 2,620 cotyledons cultured on high salt medium, 3 survived, showed sustained growth and regenerated shoots. They were multiplied by axillary bud culture on NaCl free medium. The salt-selected shoots retained salt tolerance following 3 month of growth and multiplication on control medium. While two of these somaclones flowered and set seeds, third one grew slowly, had abnormal leaf morphology and was sterile. The seed of the two fertile plants were sown in the field to raise R₁ segregating generation. Data were recorded for field, other agronomic components and oil content. The somaclonal lines, both selected salt-tolerant and non-selected, showed tremendous amount of variation for all the characters studied. One of the two tolerant somaclones invariably showed reduced height, longer reproductive phase and higher 1000 seed weight. Based on the agronomic performance of R₁ plants of these somaclones, some plants were selected and their progeny were evaluated for agronomic performance under standard field conditions and salt-tolerance in the greenhouse using sand pot culture method. Most of the lines bred true for their specific characteristics. In the greenhouse, selected salt-tolerant somaclones (SR-2 and SR-3) performed better for plant growth, yield and other agronomic traits at higher salt treatments, indicating thereby that salt-tolerance trait selected in vitro was expressed in the whole plants and is genetically stable and transmitted onto the progeny. The two tolerant lines, however, differed in their salt-tolerance during vegetative and reproductive phases as indicated by their salt-tolerance and stress susceptibility indices. The mechanism of salt-tolerance is not clear and needs to be further investigated.     

Absence of a genetic relationship between salt tolerance during seed germination and vegetative growth in tomato

Two approaches were used to determine the relationship between salt tolerance during seed germination and vegetative growth in tomato. First, F₄ progeny families of a cross between a breeding line, ‘UCT5’ (salt sensitive at all developmental stages), and a primitive cultivar, ‘PI 174263’ (salt tolerant during germination and vegetative growth), were evaluated in separate experiments for salt tolerance during germination and vegetative growth. There were significant differences among the F₄ families in both the rate of seed germination and the plant growth (dry matter production) under salt stress. There was, however, no significant correlation between the ability of seeds to germinate rapidly and the ability of plants to grow under salt stress. In the second approach, selection was made for rapid germination under salt stress in an F₂ population of the same cross and the selected progeny was evaluated for salt tolerance during both germination and vegetative growth. The results indicated that selection for salt tolerance during germination significantly improved germination performance under salt stress; a realized heritability estimate of 0.73 was obtained. Selection for salt tolerance during germination, however, did not affect plant salt tolerance during vegetative growth; there was no significant difference between the selected and unselected progeny based on either absolute or relative growth under salt stress. Obviously, in these genetic materials, salt tolerance during germination and vegetative growth are controlled by different mechanisms. Thus, to develop tomato cultivars with improved salt tolerance, selection protocols that include all critical developmental stages would be desirable.     

In vitro selection of wheat callus tolerant to high levels of salt and plant regeneration

Summary Embryogenic calli isolated from immature embryos of four wheat cultivars were subjected to three in vitro selection methods for salt tolerance. The effect of NaCl on the selected and unselected cell lines has been investigated. The results indicated that the relative growth rate of callus decreased as the concentration of NaCl increased in both callus lines. The selected callus line gave a higher growth weight in the presence of NaCl in the medium and was highly significant as compared with unselected callus line across medium protocols in all wheat cultivars. The dry weight of both kinds of callus lines of all wheat cultivars increased markedly with increasing NaCl concentration in most cases. The Na⁺ and Cl^- contents of both callus lines were increased with increasing salinity levels while K⁺ content was decreased. The selected callus line of each cultivar at the same salinity level produced significant amounts of Na⁺, K⁺ and Cl^- higher than the unselected callus line in most salinity levels. However, the unselected callus lines of the cultivars Giza-157 and Sakha-90 at the same salinity level produced significant amounts of K⁺ higher than the selected callus line in most salinity levels. The proline content of both kinds of callus lines for all wheat cultivars was increased with increasing salinity level. However, the selected callus line gave a significantly higher proline content than the unselected callus line in all wheat cultivars at the same Salinity level. Results from the in vitro selection for NaCl tolerance showed that the stepwise method of increasing NaCl in the medium was more effective for plant regeneration than other methods.     

Relationships between cold- and salt-tolerance during seed germination in tomato: Analysis of response and correlated response to selection

Seeds of F₂ progeny of a cross between a slow-germinating (UCT5) and a fast-germinating tomato line (PI120256) were evaluated for germination under non-stress (control), cold-stress and salt-stress conditions, and in each treatment the most rapidly (first 5%) germinating seeds were selected, grown to maturity and self-pollinated to produce F₃ progeny. The selected F₃ progeny from each experiment were evaluated for germination in each of the three treatments, and compared with germination rate of unselected F₃ progeny. Selection for rapid seed germination was effective under cold stress and salt stress, but not effective under non-stress conditions. Furthermore, selection in either cold-stress or salt-stress treatment significantly improved progeny germination rate under both cold-stress and salt-stress treatments, as well as the non-stress treatment. The results support the suggestion that the same genes contribute to rapid seed germination under cold-, salt- and non-stress conditions. In practice therefore, selection for rapid seed germination under a single-stress environment may result in progeny with improved seed germination under a wide range of environmental conditions. Furthermore, to improve germination rate under non-stress conditions, it may be more effective to make selections under a stress treatment.     

Genetic relationships among cold, salt and drought tolerance during seed germination in an interspecific cross of tomato

Seed of BC₁ progeny of an interspecific cross between a slow germinating Lycopersicon esculentum breeding line(NC84173; maternal and recurrent parent) and a fast germinating L.pimpinellifolium accession (LA722) were evaluated for germination under cold stress, salt stress and drought stress, and in each treatment the most rapidly germinating seeds (first 2%) were selected. Selected individuals were grown to maturity and self-pollinated to produce BC₁S₁ progeny families. The selected BC₁S₁ progeny from each experiment were evaluated for germination rate in each of a non stress (control),cold-, salt- and drought-stress treatment, and their performances were compared with those of a non selected BC₁S₁population in the same treatments. Results indicated that selection for rapid seed germination in each of the three stress treatments was effective and significantly improved progeny germination rate under all three stress conditions. The results support the suggestion that same genes might control the rate of seed germination under cold, salt and drought stress. Furthermore, selection in each of the three stress treatments resulted in improved progeny seed germination rate under nonstress conditions, suggesting that genetic mechanisms that facilitate rapid seed germination under stress conditions might also contribute to rapid germination under nonstress conditions. In practice, therefore, selection for rapid seed germination under a single stress environment may result in progeny with improved seed germination under a wide range of environmental conditions. Furthermore, to improve germination rate under nonstress conditions, it might be more efficient to make selections under stress conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Effect of Different Shade Levels on Growth and Tuber Yield of Sweet Potato: II. Tuber Yield

Eight sweet potato cultivars ( Ipomoea batatas Lam.) were grown under four different light regimes (0, 26, 42 and 60 % light reduction (LR)) at two experimental sites of the International Potato Center (CIP) in Peru during the 1990 and 1991 growing season. Increasing shade diminished the tuber yield of five cultivars, two showed a tolerance for slight (26 % LR) and moderate (42 % LR) shade and one had the same yield in full sunshine and slight shade. Shade mainly reduced the sink-size (tubers m ⁻²) of sweet potato and to a lesser extent the sink-strength. The growth of the plant top was hardly affected by shade; slight shade even favoured shoot development of some cultivars. The plant top was the stronger sink under shade conditions and tuber yield was not only reduced by lesser assimilate production as a whole but also by an altered assimilate partitioning.     

The potential of selection and breeding for improved salt tolerance in lucerne (Medicago sativa L.)

Summary Four cultivars of Medicago sativa L. were subjected to selection for improved salt tolerance using a salinized solution culture technique at 250 mM NaCl. Selections were made after two weeks growth, based upon seedling shoot length differences. High (shoot lengths 14–31 mm) and low (7–12 mm) selection lines were established. Unselected shoot lengths ranged from 0–11 mm. Selection intensities ranged from 0.17% to 0.22% for the high selection lines, and from 0.30% to 1.05% for the low selection lines.Eleven selected plants from cv. CUF 101, and 10 from Local Syria were grown on and polycrossed. A sample of progeny seed from each was grown at 8 NaCl concentrations in solution cultures. Selected line seedlings produced shoots at 225, 250, 260, and 275 mM NaCl, whereas unselected material failed to grow above 225 mM NaCl. A second cycle of selection at 280 mM NaCl with these two cultivars achieved selection intensities of 0.21% and 0.45% for high and low selection lines, respectively. Selected lines grew and produced shoots at 300 mM NaCl.Seedlings derived from 1st and 2nd selection cycles and unselected control material were grown for 6 weeks at 0, 150, 175, and 200 mM NaCl in a sand culture experiment. The high selection line produced significantly greater shoot fresh weight, dry weight, and % live shoot weight than the unselected control material. Clearly selection as practised here can isolate individual seedlings having enhanced genetically based tolerance to NaCl, which is manifest in mature plants derived from polycrossing those selected individuals.     

Identification of pearl millet [Pennisetum glaucum (L.) R. Br.] lines tolerant to soil salinity

Crop tolerance to salinity is of high importance due to the extent and the constant increase in salt-affected areas in arid and semi-arid regions. Pearl millet (Pennistum glaucum), generally considered as fairly tolerant to salinity, could be an alternative crop option for salt affected areas. To explore the genotypic variability of vegetative-stage salinity tolerance, 100 pearl millet lines from ICRISAT breeding programs were first screened in a pot culture containing Alfisol with 250 mM NaCl solution as basal application. Subsequently, 31 lines including many parents of commercial hybrids, selected from the first trial were re-tested for confirmation of the initial salinity responses. Substantial variation for salinity tolerance was found on the basis of shoot biomass ratio (shoot biomass under salinity/ non-saline control) and 22 lines with a wide range of tolerance varying from highly tolerant to sensitive entries were identified. The performance of the genotypes was largely consistent across experiments. In a separate seed germination and seedling growth study, the seed germination was found to be adversely affected (more than 70% decrease) in more than half of the genotypes with 250 mM concentration of NaCl. The root growth ratio (root growth under salinity/control) as well as shoot growth ratio was measured at 6 DAS and this did not reflect the whole plant performance at 39 DAS. In general, the whole plant salinity tolerance was associated with reduced shoot N content, increased K⁺ and Na⁺ contents. The K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios were also positively related to the tolerance but not as closely as the Na⁺ content. Therefore, it is concluded that a large scope exists for improving salt tolerance in pearl millet and that shoot Na⁺ concentration could be considered as a potential non-destructive selection criterion for vegetative-stage screening. The usefulness of this criterion for salinity response with respect to grain and stover yield remains to be investigated.     

Root Growth of a Salt Susceptible and a Salt Resistant Rice (Oryza sativa L.) During Seedling Establishment Under NaCl Salinity

The salt susceptible rice ( Oryza sativa L.) cv. Jaya and salt resistant cv. Damodar seed germination and seedling growth rates were studied in laboratory and field conditions. The effect of salinity on seed germination, shoot and root length, seedling vigour index (SVI) and increase in the root: shoot length ratio in the laboratory was relatively more in cv. Jaya than in cv. Damodar. The relative susceptibility to salinity was more in cv. Jaya than in cv. Damodar in the field also. However, their responses varied with growth period. The root: shoot length and fresh and dry weight ratios increased with salinity at 15 days in cv. Jaya. The root: shoot fresh and dry weight ratio decreased with salinity at 15 days in cv. Damodar. However, the root: shoot fresh weight ratio decreased with salinity at 25 days in the susceptible cv. Jaya. The root and shoot length fresh and dry weight of cv. Damodar was enhanced at 0.5% (w/v) NaCl treatment compared to the control seedlings at 25 days. SVI in cv. Jaya decreased with salinity in the laboratory and field conditions. SVI in cv. Damodar, SVI showed little change at 15 days but decreased with salinity of 1–3% NaCl with an enhancement at 0.5% NaCl level in the laboratory and at 25 days in field conditions.     

水稻籼型不育系萌发期和幼苗期的耐盐性评价

为了鉴定水稻籼型不育系在不同生育阶段的耐盐性,筛选出适合耐盐杂交水稻新组合测配的强耐盐不育系,笔者分别在萌发期、幼苗期对8个水稻籼型不育系进行耐盐性鉴定,以耐盐品种FL478、盐敏感品种IR29为对照。结果显示：盐胁迫对水稻种子的萌发起到抑制作用,抑制效应随盐浓度的提高而增强,10 g/L NaCl浓度胁迫能较好反映水稻不育系萌发期耐盐性的差异。‘沪旱7A’、Y58S在萌发期的耐盐性最好,与FL478均属于1级,具极强的耐盐性;‘荃9311A’的盐害级别为3级,具强耐盐性。盐胁迫对水稻幼苗的生长也起到明显的抑制作用,8 g/L NaCl浓度胁迫下的枯叶率性状能较好反映水稻不育系幼苗期耐盐性的差异,‘沪旱11A’与耐盐对照FL478耐盐性相仿。     

5种生物制剂对马铃薯种薯萌芽、极端天气下植株生长和产量性状的影响

旨在满足马铃薯生产中茬口衔接、机械化生产技术应用、不利气候下稳产等对马铃薯出苗早、齐、壮的需求,以‘费乌瑞它’为供试品种,用基于有益活菌或工程菌提取物的5种生物制剂进行种薯处理,对多重性状进行了对比分析。5种生物制剂较常规化学制剂,均能够不同程度地促进种薯萌芽和芽根同生,出苗期提前2~7天,播种后49天的出苗率提高3.33%~17.78%。其中,表现最好的为酵母核苷酸衍生物和VDAL,种薯萌发和生根均显著高于对照。霜冻后,生物剂拌种处理在恢复前期促进植株生长,由此促进恢复后期的块茎发育,较常规化学处理增产8.39%~24.03%,体现了不同程度的保产效果。多马道黑、酵母核苷酸衍生物、根肽和VDAL体现出较好的保产效果,可作为种薯处理剂投入马铃薯生产。     

Genetic analysis of low-temperature tolerance during germination in tomato, Lycopersicon esculentum Mill.

The genetic basis of low-temperature tolerance during germination of tomato seed was investigated using two approaches. First, a cold-tolerant (PI 120256) and a cold-sensitive tomato cultivar (UCT5) and their reciprocal F₂, F₃ and BC₁ progeny (total of 10 generations) were evaluated for germination at a low (11 ± 0.5°C) and a high (control) temperature 20 ±0.5° C) Weighted least-square regression analysis indicated that in the low-temperature treatment most of the variation resulted from additive genetic effects, and dominance and epistatic interactions were nonsignificant. Partitioning of the total genetic variance into those attributable to the effects of embryo, endosperm, testa and the cytoplasm indicated that additive effects of endosperm and embryo could individually account for 80% and 77% of the total variance, respectively. In the control treatment, greater than 60% of the variation could be explained by individual additive effects of endosperm or embryo and ? 27% of the variation could be explained by embryo dominance effects. Across generations, there was a positive correlation (r = 0.78, P < 0.01) between germination in the control and low-temperature treatments and there were no significant genotype × temperature interactions. The results indicate the presence of similar or identical genes with predominantly additive effects on germination under both low and high temperatures. In the second approach, the effectiveness of directional phenotypic selection to improve tomato cold tolerance during germination was evaluated by selecting (in an F₂ population of the same cross) the fastest germinating seeds under low temperature and comparing the germination of the selected F₃ progeny with germination of an unselected F₃ population. The results indicated that selection was highly effective and significantly improved germination performance of the progeny; a realized heritability of 0.74 was obtained for low-temperature tolerance during germination. It is concluded that in these tomato lines germination under low temperature is genetically controlled, with additivity being the major genetic component, and thus the trait can be improved by phenotypic selection.     

Breeding the common bean (Phaseolus vulgaris L.) for resistance to bean common mosaic virus: alternatives to backcrossing

A series of field experiments was undertaken in order to determine whether resistance to bean common mosaic virus (BCMV) could be incorporated into genotypes of the common bean (Phaseolus vulgaris L.) suitable for cultivation in Zimbabwe without recourse to backcrossing. Six inbred genotypes carrying the resistance-conferring alleles at the loci I and Bc-3 were crossed with five locally-adapted inbred genotypes. The first experiment comprised F₃ progeny rows, each derived from a single unselected F₂ plant, the second, F₃ bulks selected for resistance, and the third, a comparison of selected and unselected F₂-derived F₄ lines. The number of days to flowering and to maturity, the incidence of mosaic and necrosis symptoms, seed yield and seed size were recorded. There was evidence that late flowering and maturity were associated with BCMV resistance in some crosses, though not strongly enough to present an obstacle to plant breeding. The incidence of virus symptoms and seed yield were influenced by genetic factors additional to the major resistance genes, and variation in seed yield was present not only between bulk populations of crosses, but also between single-row plots of lines within crosses. This indicates that early-generation selection for yield in the presence of BCMV, even among progeny selected for BCMV-resistace, is likely to be effective. However, the variation in yield among F₄ lines was least in the highest-yielding crosses, which may represent a limit to successful selection for yield. Seed size was partly under additive genetic control, but there was also evidence of non-allelic interactions. There was no association between large seed size, preferred by consumers, and susceptibility to BCMV in the progeny, indicating that the association between these characters in the parent lines is fortuitous and will not present an obstacle to plant breeding. It is noted that a considerable amount of useful genetic information can be obtained without recourse to elaborate crossing schemes, provided that unselected progeny are included in experiments as controls. The evidence presented indicates that resistance to BCMV can be combined with appropriate values of maturity date, yield and seed size without the need for backcrossing.     

The Response of Sweet Potato (Ipomoea batatas Lam.) to Inter- and Relay-cropping with Maize (Zea mays L.)

Four sweet potato cultivars were inter- and relay-cropped with maize at two locations in Peru. Increasing interspecific competition drastically reduced tuber yields of all cultivars; fewer tubers m ⁻² were produced and no tolerant genotype was identified. Likewise the mean tuber weight declined linearly for two cultivars when competition became severe. Shoot development was less affected. Under intense competition the plant top was favoured in assimilate partitioning to the detriment of tuber formation. Overall reduction in assimilate production due to mixed cropping was the major cause of yield loss. Various intercropping combinations were found with the same productivity but distinct proportions of the component crops (sweet potato + maize). Land equivalent ratio (LER) exceeded sole crop productivity only for the combinations with the highest maize yields. Biomass production was clearly increased by intercropping but there was no increment in marketable yields. Relay-cropping reduced tuber and maize yields and had the lowest productivity of all combinations tested.     

Seed priming improves germination in saline conditions for Chenopodium quinoa and Amaranthus caudatus

Seed priming has proved to be an effective method in imparting stress tolerance to plants using natural and/or synthetic compounds to treat the seeds before germination. The present work aimed to evaluate the effectiveness of priming treatments in seeds of Chenopodium quinoa and Amaranthus caudatus to improve germination under NaCl. Species‐specific protocols for seed hydropriming and osmopriming were established by germinating seeds under different water potentials and creating seed imbibition curves. Primed seeds were then germinated under different concentrations of NaCl, and the effect of priming was analysed based on the parameters, such as final germination percentage (FGP), germination index (GI) and mean germination time (MGT). Seed hydropriming and osmopriming caused significant improvements in germination velocity and uniformity, reflected in high FGP, high GI and reduced MGT under salinity. C. quinoa had a higher tolerance to salinity than A. caudatus during seed germination. Improved germination in salinity resulted from osmopriming seeds with solutions of low water potential for A. caudatus, while for C. quinoa, this effect was achieved from hydropriming and osmopriming seeds with solutions of high water potential. Primed tolerance to moderate salinity was achieved for A. caudatus, and for both species, the salinity threshold for germination to occur was slightly broadened.     

盐胁迫对植物的影响及植物盐适应性研究进展

盐分是影响植物生长及发育的重要环境因素之一。本文综述了盐胁迫对种子萌发,生长发育及光合作用的影响,并从植物自身结构、活性氧清除、渗透调剂物质、离子稳态等方面评述植物对盐分的适应性机制。     

Methods used in evaluating potato seedlings

7. Summary The maintenance and assessment of potato seedlings in 5 consecutive years of trial are described.In the first year single tubers from each plant in a progeny are planted in single rows across the drills (fig. 2). After selection the haulms are killed and 6 tubers per approved seedling are kept.In the second year the unit is 6 tubers per seedling and the seedlings are grouped according to the progeny to which they belong. A standard variety is planted after each group of 9 seedlings. Tubers are harvested towards the end of August and kept in air-cooled stores.In the third year, 18 tubers are planted in 3 drills of 6 plants. 6 tubers of each seedling are planted in a virus-infested area.In the fourth year, seedlings in plots of 36 tubers are compared with nearly all the potato varieties cultivated in the Netherlands. Haulms are not destroyed but elsewhere 40-tuber plots are laid down for seed production.In the fifth year the method of trial is similar to that of the fourth year but in addition seedlings are included in the trials described by Mr J. A. Hogen Esch (Euphytica 2, 1953: 211–233).     

Effect of selection for pollen grain size on various traits in common bean

Summary Selection among microgametophytes usually exploits variation in pollen grain germination. Studies of variation in pollen grain size in common bean (Phaseolus vulgaris L.) suggested that selection for size might lead to changes in sporophytic traits. To determine whether microgametophytic selection based on size would affect pollen grain size in subsequent generations or sporophytic traits that were correlated with pollen grain size, pollen grains from three crosses were separated into two size categories by sieving and then used to pollinate cv. Diacol Calima. Selection resulted in changes in pollen grain diameter for pollen from F₁, F₂ and F₃ plants for all crosses. In vitro germination indicated no differences between vigor of large and small grains, but extraction and sieving reduced germinability. F₁ seed from two of the crosses with size-selected pollen varied in weight according to pollen grain size, but in subsequent generations, the effect disappeared. Both size categories of selected pollen resulted in F₂ progeny with reduced numbers of seeds per pod as compared to controls, suggesting that the size selection process may have resulted in indirect selection for traits reducing seed set. The overall results suggested that genes determining pollen grain size in bean have little or no effect on sporophytic traits such as seed size and seed yield.     

Selection for cold chipping genotypes from three early generations in a potato breeding program

Chipping potatoes are an important market for the processing industry. Of the traits influencing chip quality,chip color is market limiting since other traits have diminished value without light chip color. Cold (4 ^°C) storage can reduce storage losses and cultivars producing light colored chips directly from cold storage are needed for this reason. Selection for cold chipping cultivars is traditionally practiced by visual evaluation of progeny the first few years in the field, followed by selection for cold chipping in years 4–5. Early generation selection for cold chipping may reduce cultivar development time by identifying good chipping progeny, families and parents earlier in the breeding cycle. Progeny from 175 4x × 4x families were evaluated from three early generations. They were greenhouse grown tubers (GGT) evaluated after6 mo. storage using randomly selected progeny, and field grown single hills propagated from either seedling transplants (FTR), or from greenhouse grown tubers (FGT). Progeny from field grown generations were selected first by visual evaluation, and then by random selection and chipped after6 mo. (visual selections) or 3 and 6 mo. storage (random selections). Cold chipping progenies were found in all three early generations. The earliest generations for selection are GGT or FTR, but may be less efficient than FGT. Correlations suggest that reliable parent and family selection is possible using GGT data. Visual selection eliminated 4/5 of the good chipping progeny, while identifying 8 of 11,714 genotypes combining visual merit and cold chipping potential. Increased genetic variation and sexual polyploidization are possible strategies for increasing the number of desirable genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic gain from early generation selection for cold chipping genotypes in potato

Early generation selection for chip colour may accelerate potato chipping cultivar development. The research objective was to measure the response from early generation selection for light potato chip colour. Progeny from 175 4×× 4× families were propagated to the field using greenhouse grown tubers or seedling transplants. Tubers from progeny were made into potato chips after 3 and 6 months’ storage at 4° C. Chip colour was rated as 1 = light to 10 = dark. Genotypes were categorized as retained (≥ 4) or discarded (> 4) based on the 6‐month chip colour, then field grown a second year at two locations and re‐evaluated for chip colour. Positive selection responses resulted, but were lower in the seedling transplants. Interaction between genotype and environment, and genotype and storage duration reduced responses. Selected genotypes should be evaluated over multiple environments and storage conditions to insure reliable performance. Expanding variation by introgressing favourable alleles from wild species may further enhance breeding success.