Inheritance of salt tolerance in rice

Summary The genetic behavior of salt tolerance was studied in artificially salinized conditions at the International Rice Research Institute.Divergent selection, carried out at a salinity level where the ECe was 15.2 mmhos/cm at 25 C in F₃ lines from two crosses confirmed the effects of salt tolerance on F₄ progeny with realized heritability values of 0.39 and 0.62, respectively.In a cross between two tolerant cultivars there was clear over-dominance for tolerance, despite the high environmental fluctuation which resulted in a low genetic response as indicated by a low but significant repeatability of 0.20–0.25, and many progeny lines more tolerant than the parents were recovered. The superior tolerance of these progenies compared to the parents was confirmed subsequently at 3 different salt levels. In the same experiment a cross between tolerant and susceptible cultivars produced some progeny of comparable tolerance with tolerant sources.In a 6×6 diallel cross experiment with two tolerant, moderate, and susceptible varieties each, both general and specific combining ability were significant.The findings indicate the possibility of breeding rices more tolerant than existing tolerant cultivars through cumulative crosses of tolerant cultivars. Further improvement can be attained by crossing highly tolerant lines with donors of good agronomic traits and pest and disease resistance.     

Nuclear genetic control of variation in simazine tolerance in oilseed brassicas

Summary Substantial variation in tolerance to the triazine herbicide simazine was observed among a wide range of Brassica napus cultivars grown in a hydroponic screening system. None of these cultivars was as tolerant of are simazine treatment as the Canadian cultivar Triton which carries cytoplasmic gene(s) which confer a high level of resistance through their modification of chloroplast membranes to which triazine herbicides normally bind. A field study showed that the most tolerant cultivar Haya had a significantly higher yield than Triton in both handweeded plots and plots treated with 1000 ml/ha simazine. This finding supported other observations that the yield potential of cultivars such as Triton is substantially reduced because of the impairment of photosynthesis by cytoplasmic gene(s) for triazine resistance. A slight reduction in the yield of Haya with an increase in simazine concentration from 500 to 1000 ml/ha suggested that further increases in simazine concentration required for optimal weed control are likely to have a detrimental effect on the yield of Haya and other tolerant cultivars. Genetic analyses of variation in simazine tolerance in populations derived from crosses among cultivars representative of the range in tolerance indicated that the narrow-sense heritability of tolerance was of sufficient magnitude to allow for isolation of genotypes tolerant of higher simazine concentrations. These could be utilized in developing high yielding cultivars in areas of southern Australia where simazine treatment is necessary for effective weed control in Canola crops.     

Comparative study of the Nicotiana species with respect to water deficit tolerance during early growth

Sixty Nicotiana species were examined for tolerance against various osmotica for seed germination and seedling growth in vitro. The species showed a wide variety of tolerance, and based on the results of the in vitro tests, 31 species were selected and further evaluated for salt and drought tolerance in a glasshouse. The degrees of tolerance of germination among the 57 species toward NaCl were approximately related to those toward mannitol, indicating that the osmolarity plays a majorrole in seed germination. However, the responses during the seedling growth differed in NaCl and mannitol or drought, and there was no correlation between salt and drought tolerance. Based on the responses in vitro and in the glasshouse, N. paniculata and N. excelsior were selected as the salt tolerant species, and N. arentsii as the salt sensitive species. The degrees of accumulation of dry matter and of Na⁺ in the leaves were different in the two tolerant species; during NaCl treatment, N. paniculata and N. arentsii accumulated less dry matter relative to the control plants than N. excelsior, and N. paniculata accumulated more Na⁺ in its leaves than N. excelsior and N. arentsii. It is assumed that the two salt tolerant species have different mechanisms for tolerance to the salt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aluminum tolerance in barley: Methods for screening and genetic analysis

Aluminum (Al) tolerance in roots of two cultivars of barley was studied using hematoxylin staining and root re-growth procedures. This study was performed in two F₂ segregating populations originated from crosses between the tolerant FM-404 and sensitive Harrington cultivars. The F₂ progeny analysed with hematoxylin staining revealed a segregation ratio of 3 tolerant: 1 sensitive, showing that the Al tolerance is controlled by a single gene with complete dominance for tolerance. The root re-growth measures do not confirm the 3:1 ratio. This last result can be explained due to the occurrence of genes that affect root growth rate or to the difficulties found in the evaluation of root re-growth. Barley has a complex root system, which makes it difficult to measure root re-growth after an extended period in nutrient solution. Due to the simplicity, reliability and better precision, the hematoxylin staining is the best procedure to determine the Al tolerance and its inheritance in barley. This revised version was published online in August 2006 with corrections to the Cover Date.     

Responses of wheat and barley genotypes to toxic concentrations of soil boron

Summary The growth and yield of seven wheat and two barley cultivars or lines, previously found to show different degrees of boron tolerance under field conditions, were compared in a pot experiment at a range of soil boron treatments. Soil treatments ranged up to 150 mg/kg applied B. Extractable B in soils ranged up to 103 mg/kg.At the highest B treatment seedling emergence was delayed, but the percentage emergence was not reduced. The degree of boron toxicity symptom expression varied between the wheat cultivars and lines, with the two most tolerant, Halberd and (Wq^*KP)^*WmH)/6/12, displaying the least symptoms.The concentration of boron applied to the soil which produced a significant depression of growth and yield varied between cultivars. For example, the yield of (Wq^*KP)^*WmH)/6/12 was not affected at the 100 mg/kg applied boron treatment, while the grain yield for (Wl^*MMC)/W1/10 was significantly reduced at the 25 mg/kg treatment.There was a linear increase in boron concentration in tillers at the boot-stage with increasing concentration of boron in the soil. The most boron tolerant genotypes had the lowest tissue boron concentrations in each of the treatments. Halberd and (Wq^*KP)^*WmH)/6/12 had approximately half the boron concentrations of the more sensitive genotypes at the 25 and 50 mg/kg treatments. Differential tolerance of boron within the tissue was also observed. Both Stirling and (Wl^*MMC)/W1/10 had significantly reduced total dry matter and grain yields at the 25 mg/kg treatment, while the concentrations of boron in boot stage tillers at this treatment were 118 and 100 mg/kg, respectively. On the other hand, Halberd and (Wq^*KP)^*WmH)/6/12 had tissue boron concentrations of 144 and 131 mg/kg, respectively, at the 50 mg/kg treatment but yield was unaffected.The relative responses in the pot experiment, for wheat, were in close agreement with field results. Halberd and (Wq^*KP)^*WmH)/6/12 had the highest grain yields, with the lowest concentrations of boron in the grain when grown under high boron conditions in the field. In pots these two genotypes proved to be the most tolerant of boron. For barley the advantage in grain yield in the field, expressed by WI-2584 compared with Stirling, was not repeated in pots. WI-2584 was, however, more tolerant than Stirling on the basis of total dry matter production.The results show that useful variation in boron tolerance exists among wheat, and that breeding should be able to provide cultivars tolerant to high levels of boron.     

A simple,rapid and reliable bioassay for evaluating seedling vigor under submergence in <Emphasis Type="Italic">indica</Emphasis> and <Emphasis Type="Italic">japonica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Submergence is a major stress causing yield losses particularly in the direct-seeded rice cultivation system and necessitates the development of a simple, rapid and reliable bioassay for a large scale screening of rice germplasms with tolerance against submergence stress. We developed two new bioassay methods that were based primarily on the seedling vigor evaluated by the ability of fast shoot elongation under submerged conditions, and compared their effectiveness with two other available methods. All four bioassay methods using cultivars of 7 indica and 6 japonica types revealed significant and consistent cultivar differences in seedling vigor under submergence and/or submergence tolerance. Japonica cultivars were more vigorous than indica cultivars, with Nipponbare being the most vigorous. The simplest test tube method showed the highest correlations to all other methods. Our results suggest that seedling vigor serves as a submergence avoidance mechanism and confers tolerance on rice seedlings to flooding during early crop establishment. A possible relationship is discussed between seedling vigor based on fast shoot elongation and submergence tolerance defined by recovery from submergence stress.     

An evaluation of seed and seedling drought tolerance screening tests in wheat

Summary A series of experiments was performed in order to evaluate the significance of seed germination and seedling growth in osmotic media as screening methods for drought tolerance.Ten spring wheat (Triticum aestivum L. em Thell.) and one durum wheat (Triticum durum Desf.) were tested under controlled environments, using polyethylene glycol-6000 (PEG) solutions as the moisture stress inducing media.Tolerance in the rate of endosperm utilization, under stress, prior to the onset of germination varied among cultivars.Germination rate or injury to germination at various concentrations of PEG differed significantly among cultivars. Cultivar rating with respect to injury to germination changed with stress levels. Injury to germination did not correlate with endosperm utilization rate in PEG or in water.Germinating seedlings were tolerant to extreme desiccation up to the stage of emergence of the first leaf from the coleoptile.Growth of photosynthesizing seedlings was monitored as they were carried through an increasing concentration gradient of PEG solutions, ranging from –5.9 to –11.3 bars of water potential. Cultivars significantly differed in seedling growth tolerance to increasing levels of water stress. Seedling growth tolerance across cultivars was not correlated with their germination responses under srress.It is concluded that tolerance to water stress in growing seedlings can be screened for by using PEG-containing nutrient solutions. It can not be predicted from germination tests in osmotica.Work was done under a US-Israel Binational Science Foundation (BSF) Grant no. 1654/78.Contribution from Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 192-E, 1979 series.     

Race 1 fusarium wilt tolerance on banana plants selected by fusaric acid

Summary The selection of tolerant variants to race 1 fusarium wilt of banana was carried out through the effects of fusaric acid onin vitro banana multiple bud clumps (MBCs). The MBCs of Maçã cultivar (Musa sp., AAB, Silk), which is susceptible to the race 1 fusarium wilt, were used. And, Nanicão cultivar (AAA, Cavendish subgroup) was used in the tolerant tests as control of a disease tolerant variety. Firstly, to aim at determining an appropriate concentration of the toxin for the tolerant selection, the MBCs were cultured on the Modified Murashige & Skoog medium supplemented with 0.05 to 1.6 mM fusaric acid. The growth on both cultivars was completely inhibited on the medium containing 0.1 mM fusaric acid.Tolerant variants of Maçã were, then, selected with 0.1 mM fusaric acid after chemical mutagen treatment. The results showed an increased tolerance of the selected Maçã plants to the race 1 fungus in greenhouse tests. In vitro selection by fusaric acid is a very useful method for obtaining fusarium disease tolerance, although the tolerance mechanism of the selected plants may be different from that of existing tolerant cultivars.     

Genes conferring low seedling reaction to Mexican pathotypes of Puccinia recondita f. sp. tritici,and adult-plant responses of recent wheat cultivars from the former USSR

Fifty-five spring bread wheat (Triticum aestivum L.) cultivars, mostly released between 1975 and 1991 in eight leaf rust-prone spring wheat growing regions of the former USSR, were tested in the seedling growth stage for reaction to 15 Mexican pathotypes of Puccinia recondita f. sp. tritici. In total, seven known and at least two unknown genes were identified, either singly or in combinations: Lr3 (7 cultivars), Lr10 (14), Lr13 (5), Lr14a (1), Lr16 (1), Lr23 (3); the unknown genes were identified in 14 cultivars. The first unknown gene could be either Lr9, Lr19, or Lr25; however, the second unknown gene in 9 cultivars was different from any named gene. Twelve of the 15 pathotypes are virulent for this gene, hence its use in breeding for resistance will be limited. The cultivars were also evaluated at two field locations in Mexico with two pathotypes in separate experiments. The area under the disease progress curve and the final disease rating of the cultivars indicated genetic diversity for genes conferring adult plant resistance. based on the symptoms of the leaf tip necrosis in adult plants, resistance gene Lr34 could be present in at least 20 cultivars. More than half of the cultivars carry high to moderate levels of adult plant resistance and were distributed in each region.     

Inheritance of tolerance to barley yellow dwarf virus in oats

Summary Advanced generation random lines from crosses of tolerant x susceptible parents were studied to determine the inheritance of tolerance to barley yellow dwarf virus (BYDV) in oats Avena sativa L. Clintland 64, a susceptible oat cultivar, was crossed with the BYDV tolerant oat lines Otee, FF64/74, M921 and CI4492. Randomly selected lines were advanced to F5 or F6 by single seed descent and were tested for their reaction to BYDV at Palmerston North, New Zealand and Winnipeg, Manitoba and Ste-Foy, Quebec, Canada.The reactions of the lines to BYDV infection from each cross at the three test sites fall into a relatively continuous distribution. Two to four quantitatively inherited genes appear to contribute to the tolerance of the four tolerant oats. At Palmerston North, Clintland 64 expressed some tolerance to the virus.The correlation between the three sites was significant (P=0.01) for all crosses, ranging from 0.36 to 0.69, according to the particular cross considered. This correlation is sufficient to justify more international testing of oats for BYDV tolerance.Contribution Nos. 1163.     

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.     

Effect of Phaeosphaeria nodorum-induced seed shrivelling on subsequent wheat emergence and plant growth

Summary The bread wheat cultivars Pasqua and Katepwa, and durum wheat cultivars Kyle and D8257 were used to test the effects of sowing Phaeosphaeria nodorum-shrivelled seed. In a controlled environment, emergence, tillering, and dry weight of seedlings were compared at two sowing depths. Emergence, tillering and plant dry weights were also determined in field plots in 1992 and 1993, as were yield and thousand kernel weight (TKW) in plants inoculated with P. nodorum. Under controlled conditions the level of shrivelling did not affect emergence at depths of 25 mm and, except for Katepwa, 50 mm. Deeper seeding reduced emergence regardless of the level of shrivelling. Seeding depth did not affect dry weight of roots and shoots and the effect on tillering was inconsistent in the two years. Dry root weight was positively correlated with original seed size and decreased with level of shrivelling. In the field, seedling emergence of severely shrivelled seed was significantly lower in Katepwa and Pasqua. Tillers per plant appeared to increase with increased level of shrivelling, but was significant only for D8257 in one year. Dry tiller weight was inversely related to tillering and decreased consistently with level of shrivelling. Excepting Pasqua, in one year, yield and TKW did not differ between plots originating from plump or shrivelled seed. Inoculation with P. nodorum caused a significant reduction in TKW and yield in all cultivars but Kyle. Seed shrivelled due to P. nodorum was in general found to be as suitable as plump seed for growing a wheat crop.     

Variation in partial resistance to barley leaf rust (Puccinia hordei) and agronomic characters of Ethiopian landrace lines

An inventory of 481 lines derived from 12 Ethiopian barley (Hordeum vulgare L.) landraces and the checks was made for partial resistance to Puccinia hordei under greenhouse and field conditions at Adet, Ambo and Sinana Agricultural Research Centers in 2003 and 2004 cropping seasons in Ethiopia. The experiments were laid out in a triple lattice design. Each plot consisted of two rows of 1–m long with spacing of 0.20 m between rows. The overall mean leaf rust epidemics varied from area under disease progress curve (AUDPC) of 86 to 1,835. The disease was as high as AUDPC 1,378 on the susceptible check L94. Highly significant variations were recorded between and within the landraces/lines in leaf rust incidence, severity, days to heading, plant height, thousand seed weight and yield. Similarly, the variations between and within barley groups from three altitude areas and three ear-types were significant. Landraces 1686, 3255, 3262 and 3783 had the least and landraces 219900, 3975 and 3980 had the highest leaf rust severity. Of the 481 lines tested, 413 (86%) had significantly lower disease than the susceptible check, but not than the partial resistant check Vada. In contrast, the yields were more for lines with less disease than for those with high. The frequency of resistant landraces/lines was more in altitude 2,301–2,500 m, and irregular and two rows ear-types than in lower altitude areas and six rows ear-type. Nevertheless, the correlation and regression analysis revealed the adverse effect of the disease in the yields of barley. The 413 lines with high infection types at seedling stage and lower AUDPC under field conditions possess partial resistance to leaf rust.     

Differential tolerance to Fe and Zn deficiencies in wheat germplasm

Tolerance to Fe deficiency of wheat genotypes exhibiting differential tolerance to Zn deficiency is not known, even though the relationship between Fe nutrition and differential tolerance of wheat genotypes to Zn deficiency has been hypothesised frequently. In the present experiment, eight Triticum aestivum and two T. turigidum L. conv. durum cultivars were grown in nutrient solution deficient in either Znor Fe. Three indices of tolerance to nutrient deficiency were compared: relative [(-nutrient/+nutrient) × 100] shoot growth, shoot dry weight under nutrient deficiency and relative shoot/root dry weight ratio. Genotypes Aroona, Excalibur, Stilleto and Trident were classified as tolerant to both Zn and Fe deficiency, while durum wheats Durati and Yallaroi were sensitive to Zn deficiency and moderate to sensitive to Fe deficiency. Genotypes Excalibur, Stilleto and Trident come from the same breeding programme and have the common parent (line MEC3 =Sonora64//TZPP/YAQUI54) that could have been the donor of the genes for tolerance to Zn deficiency. When Fe-deficient, all wheat genotypes were severely chlorotic but kept producing shoot and root dry matter at a relatively high rate, making the relationship between the relative shoot growth and the relative leaf chlorophyll content poor. This is the first report of wheat genotypes exhibiting multiple tolerance to Zn and Fe deficiencies. This revised version was published online in July 2006 with corrections to the Cover Date.     

A shattering-resistant mutant of Papaver bracteatum Lindl.: characterisation and inheritance

Summary Papaver bracteatum is a potential crop for the codeine industry. Seed shattering prevailing in the species is a major problem which reduces the seed yields. A spontaneous mutant with capsules having no pores of dehiscence was isolated in an experimental field. The seed yields of this shattering-resistant mutant are lower than in plants with normal capsules but the thebaine content of the capsules from the mutant is higher. The mutation is monogenic dominant; it can be used for breeding cultivars for dual purpose-thebaine and seeds.     

Breeding and evaluation of Digitaria eriantha for improved spring yield and seed production

Summary Digitaria eriantha is a subtropical grass which is widely sown as a pasture species in South Africa and cultivars have recently been released in Australia. The species is variable in seed production and in other agronomic attributes. This paper describes a breeding program designed to combine the seed production of cv. Premier with the high productivity in winter-spring of an almost sterile genotype.Hybrids between the two accessions were either triploid and sterile, or diploid with low fertility. The F₂ to F₅ generations were selected intensively for fertility and, at two contrasting sites, for spring productivity, with both maternal and paternal selection. The F₆ generation was grown as replicated swards and yield in spring, and fertility, were used for selection of elite F₅ plants to comprise the parents of a new cultivar (cv. Advance).In evaluation trials, spring dry matter production of Advance averaged 40% higher than that of Premier. On average, seed production of Advance was 11% lower than that of Premier and botanical fertility was consistently about half that of Premier. Experimental yields of cleaned seed of Advance were up to 138 kg/ha. In commerce, seed yields of Advance are likely to be lower than those of Premier unless higher inflorescence densities than Premier can be achieved.     

Evaluation of seedling and adult plant resistance in European wheat cultivars to Australian isolates of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

A set of 105 European wheat cultivars was assessed for seedling resistance and adult plant resistance (APR) to stripe (yellow) rust in greenhouse and field tests with selected Australian isolates of Puccinia striiformis f. sp. tritici (Pst). Twelve cultivars were susceptible to all pathotypes, and among the remainder, 11 designated seedling genes (Yr1, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr27, Yr32, YrHVII and YrSP) and a range of unidentified seedling resistances were detected either singly or in combination. The identity of seedling resistance in 43 cultivars could not be determined with the available Pst pathotypes, and it is considered possible that at least some of these may carry uncharacterised seedling resistance genes. The gene Yr9 occurred with the highest frequency, present in 19 cultivars (18%), followed by Yr17, present in 10 cultivars (10%). Twenty four cultivars lacked seedling resistance that was effective against the pathotype used in field nurseries, and all but two of these displayed very high levels of APR. While the genetic identity of this APR is currently unknown, it is potentially a very useful source of resistance to Pst. Genetic studies are now needed to characterise this resistance to expedite its use in efforts to breed for resistance to stripe rust. Colin R. Wellings seconded from NSW Department of Primary Industries.     

Evaluation of seedling and adult plant resistance to leaf rust in European wheat cultivars

Summary A set of 105 European wheat cultivars, comprising 68 cultivars with known seedling resistance genes and 37 cultivars that had not been tested previously, was tested for resistance to selected Australian pathotypes of P. triticina in seedling greenhouse tests and adult plant field tests. Only 4% of the cultivars were susceptible at all growth stages. Twelve cultivars lacked detectable seedling resistance to leaf rust, and among the remaining cultivars, 10 designated genes were present either singly or in combination. Lr13 was the most frequently detected gene, present in 67 cultivars, followed by the rye-derived gene Lr26, present in 19 cultivars. Other genes present were Lr1, Lr3a, Lr3ka, Lr10, Lr14a, Lr17b, Lr20 and Lr37. There was evidence for unidentified seedling resistance in addition to known resistance genes in 11 cultivars. Field tests with known pathotypes of P. triticina demonstrated that 57% of the cultivars carried adult plant resistance (APR) to P. triticina. The genetic identity of the APR is largely unknown. Genetic studies on selected cultivars with unidentified seedling resistances as well as all of those identified to carry APR are required to determine the number and inheritance of the genes involved, to determine their relationships with previously designated rust resistance genes, and to assess their potential value in breeding for resistance to leaf rust.     

Evaluation of barley yellow dwarf tolerance from plant traits in two winter × spring barley crosses

Summary Winter-type experimental lines from crosses of two winter-type barley cultivars with a spring-type, barley yellow dwarf (BYD) tolerant cultivar were compared in inoculated and uninoculated hill plots. Mature plants traits-winter survival, height, number of spike-bearing tillers, and biomass-were examined. The experimental lines could not be compared with the BYD tolerant parent using these diagnostic symptoms since the spring-type parent would be winterkilled. Two criteria were used to rate experimental lines for BYD tolerance: (1) nonsignificant difference between BYD-inoculated and BYD-uninoculated treatments for all traits, and (2) a BYD injury score obtained by averaging percent reduction from BYD infection for each trait.Missouri Agricultural Experiment Station Journal Paper No. 10059. This research supported in part by Anheuser-Busch, Inc, St. Louis, MO, USA.