Inbred Cultivars Research Articles

Hybrid Rice Response to Nitrogen Fertilization for Midsouthern United States Rice Production

Limited data representing the southern U.S. production area exists for N nutrition in hybrid rice (Oryza sativa L.) cultivars. Experiments were conducted to evaluate the effects of N fertilizer rates and application timings on grain and whole milled rice yield for ‘XL723’ (RiceTec, Inc., Alvin, TX) as compared with widely grown inbred rice cv. Cocodrie on clay soils and Cheniere on silt loam soils. A factorial arrangement of cultivar, preflood (PF), panicle differentiation (PD), and panicle emergence (PE) N rates were established in Louisiana, Mississippi, and Missouri for a total of three site‐years each for clay and silt loam soils. On clay soils, XL723 grain yield increased with increasing PF‐N rate reaching 12,332 kg ha−1 at a PF‐N rate of 202 kg N ha−1 ‘Cocodrie’ grain yield did not substantially increase with PF‐N >151 kg N ha−1 Averaged across cultivars, a PD‐N rate of 50 kg N ha−1 increased grain yields by 729 kg ha−1 when 101 kg N ha−1 was applied; however, as PF‐N rate increased, the effects of PD‐N were not significant. On silt loam soils, grain yields were 327 kg ha−1greater when 151 kg N ha−1 was applied PF compared with 101 kg N ha−1 Furthermore, a PE‐N rate of 50 kg N ha−1 increased grain yield by 333 kg ha−1 On clay soils, maximum whole milled rice was obtained when a minimum of 151 kg N ha−1 was applied PF and 50 kg N ha−1 was applied at PE. On silt loam soils, the 101 kg N ha−1 PF rate produced 625 mg g−1 whole milled rice for Cheniere, whereas, the greatest concentration (613 mg g−1) of whole milled rice for XL723 was produced with 202 kg N ha−1. Finally, yield potential was 17 to 20% greater for XL723 compared with the inbred cultivars; however, at equal N rates, whole milled rice was higher with conventional inbred cultivars compared with XL723. Hybrid rice can be used in the southern U.S. rice‐growing region to increase rice yield per unit of land area. Preflood N rates on hybrid rice should be equal to or greater than inbred cultivars. For practical implications, N management for hybrid rice should include a PE application to increase yield, whole milled rice, and also decrease the potential for lodging. As straw‐strength increases with new rice hybrids, PF‐N management should be reevaluated for increased yield potential.

A high-resolution, intraspecific linkage map of pepper (Capsicum annuum L.) and selection of reduced recombinant inbred line subsets for fast mapping

A high-resolution, intraspecific linkage map of pepper (Capsicum annuum L.) was constructed from a population of 297 recombinant inbred lines. The parents were the large-fruited inbred cultivar 'Yolo Wonder' and the hot pepper line 'Criollo de Morelos 334', which is heavily used as a source of resistance to a number of diseases. A set of 587 markers (507 amplified fragment length polymorphisms, 40 simple sequence repeats, 19 restriction fragment length polymorphisms, 17 sequence-specific amplified polymorphisms, and 4 sequence tagged sites) were used to generate the map; of these, 489 were assembled into 49 linkage groups (LGs), including 14 LGs with 10 to 60 markers per LG and 35 with 2 to 9 markers per LG. The framework map covered 1857 cM with an average intermarker distance of 5.71 cM. Twenty-three LGs, composed of 69% of the markers and covering 1553 cM, were assigned to 1 of the 12 haploid pepper chromosomes, leaving 26 LGs (304 cM) unassigned. The chromosome framework map built with 250 markers led to a high level of mapping confidence and an average intermarker distance of 6.54 cM. By applying MapPop software, it was possible to select smaller subsets of 141 or 93 most informative individuals with a view to reducing the time and cost of further mapping and phenotyping. To define the smallest number of individuals sufficient for assigning any new marker to a chromosome, subsets from 12 to 45 individuals and a set of 13 markers distributed over all 12 chromosomes were screened. In most cases, the markers were correctly assigned to their expected chromosome, but the accuracy of the map position decreased as the number of individuals was reduced.

Foundations of Yield Improvement in Watermelon

High yield is a major goal for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] breeders. The objective of this study was to measure yield in a diverse set of watermelon cultivars to identify high-yielding germplasm for use in breeding programs. Phenotypic variation for fruit yield in a diverse set of 80 watermelon cultivars was studied in the field in North Carolina. Yield was evaluated in replicated experiments of three environments (combinations of 2 yr and two locations), and two to four replications per environment. Plots were harvested one to two times, depending on the average maturity of the fruits at the first harvest. The highest yield overall was obtained from 'Mountain Hoosier' and 'Starbrite'. Some of the new, elite hybrid cultivars were in the top-yielding group, but there were old, inbred cultivars in the top group as well. Consistent and significant yield differences among the 80 cultivars across environments indicates genetic variation for the trait. In addition, high-yielding cultivars for use in breeding programs were identified. Watermelon breeders interested in developing new, high-yielding cultivars should make use of top performers in this study in their breeding programs.

Foundations of Yield Improvement in Watermelon

High yield is a major goal for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] breeders. The objective of this study was to measure yield in a diverse set of watermelon cultivars to identify high-yielding germplasm for use in breeding programs. Phenotypic variation for fruit yield in a diverse set of 80 watermelon cultivars was studied in the field in North Carolina. Yield was evaluated in replicated experiments of three environments (combinations of 2 yr and two locations), and two to four replications per environment. Plots were harvested one to two times, depending on the average maturity of the fruits at the first harvest. The highest yield overall was obtained from ‘Mountain Hoosier’ and ‘Starbrite’. Some of the new, elite hybrid cultivars were in the top-yielding group, but there were old, inbred cultivars in the top group as well. Consistent and significant yield differences among the 80 cultivars across environments indicates genetic variation for the trait. In addition, high-yielding cultivars for use in breeding programs were identified. Watermelon breeders interested in developing new, high-yielding cultivars should make use of top performers in this study in their breeding programs.

Can Yields of Lowland Rice Resume the Increases that They Showed in the 1980s?

The annual rate of rice yield increase in the world declined from 2.7 % in the 1980s to 1.1 % in the1990s. The continued world population increase requires resumption of the previous rate. The objectives of this paper are to review and assess rice production technologies for increased yield in the past and the current challenge on the basis of crop physiology and agronomy, and to discuss the way to increase irrigated rice yield to fulfil the expanding demand. Field experiments conducted in Kyoto, Japan and Yunnan, China showed that the best recent Chinese hybrid has a yield potential about 10 % higher than the best recent inbred cultivar in Japan. This result, and a review on recent challenges in breeding, suggested only moderate increases in the yield potential of rice genotypes in the coming decades. Contrary to the general understanding, the rapid rice yield increase in central Japan from the mid 1950s to mid 1970s was achieved mostly by improved crop and resource management. This, and the fact that farmers' contest-winning yields during 1950s and 1960s nearly doubled the current average in Japan, imply that current crop and resource management is exploiting only part of the large yield potential of rice. Some of the ways to increase yields may include components of the system of rice intensification (SRI). The extremely high yields claimed in SRI are probably not real, but its elements, which have been studied and practiced in Japan for the past 50 years, may lead to yield increases. The practice of transplanting one or two young seedlings per hill has advantages in reducing transplanting injury and increasing tiller and root numbers on lower nodes. Such advantages can be realized under direct-seeding systems, where they are applicable. The practice of applying a large amount of compost and intermittent irrigation were also adopted by many of the contest-winning farmers in the 1950s and 1960s. These practices increase roots in deeper soil layers, maintain their activities and presumably promote nitrogen (N) uptake at later stages. Remarkable progress has been made in improved N management; agronomic efficiency of N increased from about 15 kg kg-1 for a single dose at transplanting to 40 kg kg-1 for banded controlled release fertilizer. All of these technological elements will contribute to increased yield when they are rationally integrated into systems that are adaptable to regional environments.

Nitrogen economy and water productivity of lowland rice under water-saving irrigation

Water saving in irrigated lowland rice production is increasingly needed to cope with a decreasing availability of fresh water. We investigated the effect of irrigation regimes on grain yield and nitrogen (N) uptake and recovery, and the effect of N management on water productivity (grain yield/evapotranspiration (ET)). Four field experiments were carried out—three summer seasons at Tuanlin (2000–2002), China, and one dry season at Muñoz (2001), Philippines—using a hybrid for Tuanlin and an inbred cultivar for Muñoz. Several water-saving regimes were compared with continuous submergence. N fertilizer was applied at 180 kg ha −1 at Tuanlin and at 90 and 180 kg ha −1 at Muñoz and compared with a 0-N application. Grain yield ranged from 4.1 t ha −1 at Muñoz in 0-N plots to 9.5 t ha −1 at Tuanlin in 2001 with 180 kg N ha −1. Alternately submerged–non-submerged regimes showed a 4–6% higher yield than continuous submergence. Other water-saving regimes led to yield reduction. In all seasons, N application significantly increased grain yield largely through an increased biomass and grain number. Water productivity was significantly increased by N application in three out of four seasons and under limited water stress ranged from 0.70 to 1.17 in 0-N plots and from 1.27 to 1.66 kg m 3 at 180 kg N ha −1. Water-saving regimes also increased water productivity under non-water-stressed conditions compared with continuous submergence. A synthesis of the data of three seasons at Tuanlin showed that biomass and apparent N recovery declined linearly with the duration of the crop growth without submergence. We concluded that the absence of an effect of water-saving regimes was caused by shallow groundwater tables of <40-cm depth in 2000–2001 at Tuanlin and at Muñoz, whereas at Tuanlin in 2002 there was water deficit in all treatments caused by a deeper drainage. In irrigation systems with a relatively shallow water table, optimal N management is as important as water-saving irrigation to enhance water productivity.

Rice F1 hybrids: the breeding goal or a costly solution?

Whether to develop inbred cultivars or F1 hybrids is a dilemma faced by many rice (Oryza sativa L.) breeders. This could be partially answered if one could select superior recombinant inbred lines with an equal yielding ability and good quality traits from commercial F1 hybrids. Thus, it was attempted in this study to select superior inbred lines from 2 commercial F1 hybrids after application of honeycomb selection and panicle-to-row selection. The 2 F2 populations were advanced to F6 generation by both methods and, finally, 5 F5:6 lines with high yield potential and good grain quality were selected from each population and selection method and were tested in a randomised complete block design for 2 years in Kalochori, Thessaloniki, Greece. In each case the respective F1 hybrid and the check cultivar Strymonas were used as checks. Fourteen of the 20 lines selected by honeycomb selection and panicle-to-row selection from both populations exhibited a yielding ability that was not significantly different from the yield of the F1 hybrids in both years. Three of them, however, in 1 of the 2 years, had a significantly higher grain yield than the corresponding F1 hybrid. In addition, 6 of the above lines exhibited significantly higher values for more than 1 of the 4 quality traits (total milling yield, grain vitreosity, grain length, and grain length/width ratio) and they were not inferior for the remaining ones. It was concluded that application of combined selection for yield and quality could lead to the isolation of recombinant inbred lines with equal yielding ability and quality equal to or higher than the F1 hybrids. This, together with the higher cost associated with hybrid technology, indicates that the long-term goal of a rice-breeding program should be the production of superior inbred lines, unless hybrid production cost is low and quality is not critical for the particular market.

Methane transport capacity of twenty-two rice cultivars from five major Asian rice-growing countries

Of the methane (CH 4) emitted from a rice field during the growing season, 60–90% is emitted through the rice plants. In order to assess differences among cultivars, we determined the methane transport capacity (MTC) of 18 inbred varieties and 4 hybrids at seedling, panicle initiation (PI), flowering and maturity using an automatic measuring system under greenhouse conditions. All cultivars showed a large increase in MTC from seedling to panicle initiation, but differed in MTC in the succeeding growth stages until maturity. Rice cultivars could be divided into three MTC groups: (a) four hybrids showing no change in flowering to maturity; (b) eight inbred varieties (Zhong yu 906, Zhong zuo 93, Pusa Basmati 1, PR 111, CSR 13, Cisadane, Dodokan, IR72 and IR65598 (new plant type, NPT)) showing either no or minor changes in MTC from panicle initiation to flowering; and (c) nine other inbred varieties (Zhong hua 15, PR 108, Pusa 169, Membarano, Basmati 370, KDML 105, CSR 10, Dular and HTA 60) showing significant increase from panicle initiation to flowering. Groups (b) and (c) had large decreases in MTC at maturity. Differences in MTC patterns among groups were attributed to growth parameters (root, shoot, and root+shoot biomass without grains, and tiller numbers) and the development of morphological characteristics of the aerenchyma. The results suggest that in inbred cultivars representing tall, dwarf and NPT groups, an increase in root or aboveground biomass during plant growth until flowering determines the corresponding increase in MTC. Further increase or any change in plant biomass at maturity does not affect MTC. However, in the case of hybrids, a positive relationship of MTC with root, shoot and total plant biomass including grain indicate continuous development of aerenchyma with plant growth resulting in enhanced MTC. In all cultivars, tiller numbers were linearly related to MTC indicating that the number of outlets determines CH 4 transport. The relative MTC of different cultivars for the complete season ranged from 62 to 445% of IR72. These results clearly demonstrate that rice cultivars differ widely in MTC. Therefore, the use of high-yielding cultivars with low MTC (e.g. KDML 105, IR65598 and PR 108) could be an economically feasible, environmentally sound and promising approach to mitigate CH 4 emissions from rice fields.

Performance of Site‐Specific Nutrient Management for Irrigated Rice in Southeast China

Rice (Oryza sativa L.) yield increases in Zhejiang, China have slowed since 1985 despite the increasing use of hybrids and fertilizers. On‐farm experiments at 21 sites were conducted to evaluate a new approach for site‐specific nutrient management (SSNM). Field‐ and season‐specific N–P–K applications were calculated by accounting for the indigenous nutrient supply, yield targets, and nutrient demand as a function of the interactions between N, P, and K. Nitrogen applications were fine‐tuned based on season‐specific rules and field‐specific monitoring of crop N status. The performance of SSNM was tested for four successive rice crops. Compared with the current farmers' fertilizer practice (FFP), average grain yield increased from 5.9 to 6.4 Mg ha−1 while plant N, P, and K uptake increased by 8 to 14%. The gross return over fertilizer cost was about 10% greater with SSNM than with FFP. Yields were about 20% greater in late rice (hybrid cultivars) than in early rice (inbred cultivars), but SSNM performed equally better than FFP in both seasons. Improved timing and splitting of fertilizer N increased N recovery efficiency from 0.18 kg kg−1 in FFP plots to 0.29 kg kg−1 in SSNM plots. The agronomic N use efficiency (grain yield increase per kilogram fertilizer applied) was 80% greater with SSNM than with FFP. As defined in our study, SSNM has potential for improving yields and nutrient efficiency in irrigated rice. Future research needs to develop a practical approach for achieving similar benefits across large areas without field‐specific modeling and with minimum crop monitoring.

The inheritance of quantitative traits in Brassica napus ssp. rapifera (swedes) : Augmented triple test cross analyses of production characters

Two F2 triple test crosses, augmented with F3s, produced from crosses between different inbred lines of swedes (Brassica napus ssp.rapifera L.) were assessed in field trials at Dundee in 1988 and 1989,respectively. This paper reports the analyses of resistance to powdery mildew, neck length, growth cracks, sugar content and hardness; analyses of yield have been published previously. Additive genetical variation was found for all traits while non-additive variation was less important, the highest degree of dominance being 0.44 for hardness. There was evidence of additive × dominance and dominance × dominance epistasis for mildew and additive × additive epistasis for neck length and hardness. Significant,consistent reciprocal differences were found and these were particularly large for neck length and growth cracks. Sugar determination was carried out on the basic generations of the second cross, the parental lines of which showed large differences in concentration of glucose, fructose and sucrose. Directional dominance was found for high glucose but not for fructose or sucrose. The implications of these results for swede breeding are discussed and it is proposed that inbred cultivars would be a more practical option than F1 hybrids.

Methane transport capacity of rice plants. II. Variations among different rice cultivars and relationship with morphological characteristics.

Of the total methane (CH4) emitted from a rice field during the growing season, 60–90% is emitted through the rice plants. We determined the methane transport capacity (MTC) of rice plants at different physiological growth stages using an automatic measuring system under greenhouse conditions. A total of 12 cultivars (10 inbred varieties and 2 hybrids) were studied in sets of two experiments and was distinguished into three groups according to the patterns of MTC development. MTC is generally increasing from seedling stage to panicle initiation (PI), hut differs in the development from PI to maturity. While the hybrid showed a gradual increase in MTC, the inbred cultivars showed either minor changes in MTC or a drastic decrease from flowering to maturity. Among tall cultivars, Dular showed the highest MTC, followed by B40; the lowest MTC was found in Intan. High-yielding dwarf cultivars showed MTC in the descending order of IR72 > IR52 > IR64 > PSBRc 20. New plant type cultivars showed very low MTC with IR65600 exhibiting the smallest MTC at PI, flowering, and maturity. Hybrids (Magat and APHR 2) showed the largest MTC that continued to increase with plant growth. The MTC patterns were attributed to growth parameters and the development of morphological characteristics of the aerenchyma. These results suggest that in tall, dwarf, and NPT cultivars, increase in root or aboveground biomass during initial growth determines a corresponding increase in MTC. Once aerenchyma has fully developed, further increase in plant biomass would not influence MTC. However, in the case of hybrids, a positive relationship of MTC with root + shoot biomass (r = 0.672, p ≥ 0.05) and a total plant biomass including grain (r = 0.849, p ≥ 0.01) indicate continuous development of aerenchyma with plant growth, resulting in enhanced MTC. In all cultivars, tiller number, but not height, was linearly related to MTC, indicating that the number of outlets/channels rather than plant size/biomass determines the transport of CH4 . These results clearly demonstrate that rice cultivars differ significantly in MTC. Therefore, the use of high-yielding cultivars with low MTC (for example. PSBRc 20,1R65598, and IR65600) could be an economically feasible, environmentally sound, and promising approach to mitigate CH4 emissions from rice fields.

Yield Potential Trends of Tropical Rice since the Release of IR8 and the Challenge of Increasing Rice Yield Potential

ABSTRACTSince the release of IR8 in 1966, 42 additional indica rice (Oryza sativa L.) cultivars developed by the International Rice Research Institute (IRRI) for the irrigated and favorable rainfed lowlands have been released in the Philippines. The maximum yield of IR8 has been reduced by about 2 Mg ha−1 during the past 30 yr. Empirical breeding for population improvement within the indica germplasm has resulted in the maintenance of rice yield potential in the tropics of about 10 Mg ha−1. To break the yield barrier, several approaches are being explored. These include development of a new plant type (NPT) with low tillering capacity and large panicles from tropical japonica germplasm and exploitation of heterosis through intervarietal and intersubspecific hybrids. Hybrid rice between indicas increased yield potential by about 9% under the tropical conditions. The higher yield potential of indica/indica hybrids compared with indica inbred cultivars was attributed to the greater biomass production rather than harvest index. New plant type breeding has not yet improved yield potential due to poor grain filling and low biomass production. Factors that cause poor grain filling and low biomass production of the NPT lines have been identified. Selecting parents with good grain filling traits, introduction of indica genes into NPT's tropical japonica background, and a refinement of the original NPT design are expected to improve the performance of the NPT lines. Further enhancement in yield potential may be possible from use of intersubspecific heterosis between indica and NPT lines.

Heterosis in Spring Canola Hybrids Grown in Northern Idaho

Spring canola acreage has increased in the Pacific Northwest over the past 5 yr. Traditional cultivars are inbred lines, although a high proportion of newer cultivars are hybrids. This study examined the magnitude of heterosis in spring canola to determine the potential advantage of hybrid cultivars. Four inbred cultivars, with diverse geographic origins of development, were hand-pollinated in a diallel design. Performance of F1 hybrids and their respective inbred parents was evaluated under greenhouse conditions. Field trials were conducted at two locations to compare F1 hybrids and F2 progeny with inbred parents. Positive heterosis was found for yield, oil content, and oil quality, with the highest degree of heterosis observed for yield. Hybrids and F2 progeny produced higher yield than inbred parents because of increased pod number (primarily on the main raceme), larger seeds, and later maturity. However, the magnitude of heterosis observed varied between hybrids. Inbred and hybrid cultivars also were compared in the Pacific Northwest Regional Canola Variety Trials. In these trials, the most adapted hybrids had a yield advantage compared with the most productive inbred cultivars. However, average yield and oil content of hybrids were not significantly different from inbred cultivars. Inbred cultivars tended to have higher oil content and matured earlier. Introduction of hybrid canola cultivars in the Pacific Northwest region has potential to increase canola acreage and grower profit. However, choice of hybrid parents and economics of high quality hybrid seed production will be important factors in hybrid canola cultivar development and acceptance.

The inheritance of quantitative traits in Brassica napus ssp. rapifera(swedes): augmented triple test cross analysis of yield

Two augmented triple test crosses were produced from inbred lines of swede (Brassica napus ssp. rapifera L.) and assessed in field trials at Dundee in 1988 and 1989, respectively. The first cross was between lines derived from cvs. Criffel and Marian and the second between the same Criffel line and one from Bangholm Wilby. The genetic architectures of the two components of dry weight yield were clearly different. Dry-matter percentage was mainly under the control of additive genetical variation whereas fresh weight yield was under the control of additive and dominance variation. Although there was unidirectional dominance (positive [h]) for high yield, the dominance ratio was less than unity in both crosses. Dry weight yield was also under the control of genes showing both additive and dominance variation. In both crosses [h] was larger than [d] and the F1 outyielded the better parent by 14 and 12 per cent, respectively. The dominance ratio was less than unity, being 0.50 and 0.94 respectively. There was no evidence of overdominance. Whilst epistasis was not a major feature of the genetic architecture of dry matter yield and its components, there were large and unexpected reciprocal differences, particularly for fresh and dry weight yield in all TTC generations and the F3 of the first cross. These require further investigation. Finally it was concluded that it should be possible to produce inbred cultivars of swede which outyield F1, hybrids in a modest sized breeding programme because 12 and 2 per cent, respectively, of the recombinant inbred lines from the two crosses were predicted to outyield the F1.

Field performance of derived generations of transgenic tobacco

Two inbred cultivars of Nicotiana tabacum (tobacco), 'Samsun' and 'Xanthi', were transformed with the plasmid pBI 121 using Bin 19 in Agrobacterium tumefaciens. The plasmid carries the nptII gene conferring kanamycin resistance and the uidA gene encoding β-glucuronidase (GUS). Progeny carrying the genes in the homozygous condition were identified and selfed over several generations. One line homozygous for the introduced genes and one untransformed control from each cultivar were then selected and crossed reciprocally to give four families per cultivar. Seeds from each family were grown in a replicated field trial and all plants scored for a range of morphological and agronomic characters. In addition, leaf samples were taken and GUS activity measured. In the 'Samsun' material, which contained one copy of the introduced gene at a single locus and showed high levels of GUS expression, the transformed homozygote showed twice the level of GUS activity as the hemizygotes, wheareas in the 'Xanthi' line, which had a lower level of GUS, the hemizygotes showed the same level of GUS activity as the transformed homozygote. The agronomic data showed differences between the families, but the source of such differences could not be ascribed unambiguously. The results are discussed in the light of related information on gene expression and field performance from other transgenic material.

Activities of proteinases in maize and soybean roots in response to anoxic stress

This study characterized the changes in proteinase activities in maize inbred line H60 and soybean cultivar Keller roots in response to anoxia. After 24 h of anoxia, crude protein extracts from both maize and soybean root tips (10 cm) were assayed for proteinase activities at pHs ranging from 4.5 to 10.2. In anoxic roots of both maize and soybean, activities of proteinases with alkaline pH optima increased, and activities of proteinases with acidic pH optima declined. Proteinases with neutral pH increased in anoxic maize roots, but declined in anoxic soybean roots. Whether the differences in proteinase activities in anaerobic maize and soybean roots contribute to the differental susceptibility of the two species requires further study.

Is Nor region variability in wheat invariably caused by tissue culture?

In a previous study we observed extensive Nor region variability in tissue-culture derived plants of only one out of three tested wheat cultivars. This finding prompted us to further question whether or not this variability was invariably caused by in vitro culture. In the present study, the upper halves of spikes from four source plants of the inbred cultivar 'ND7532' were removed 12 days after anthesis. The immature embryos from these halves were cultured and regenerated into plants. The lower halves of the same spikes were retained on the plants to obtain mature caryopses. DNA was extracted from seedlings, cut with TaqI endonuclease, run on agarose gels, and the respective Southern blots were probed with the plasmid pTA71 to reveal the Nor region patterns. The sexual progeny of regenerants from three out of four source plants derived from the immature embryos provided Nor region patterns which were exactly identical to the patterns obtained from seedlings which germinated from the caryopses matured on the respective source spikes. The regenerants from the fourth source plant provided variable Nor region patterns. Analyses of the Nor region patterns of 21 individual seedlings germinated from caryopses of this source plant showed that 18 had a three-fragment pattern (consisting of 3.0, 2.7 and 1.9 kb fragments) while three seedlings lacked one (2.7 of 1.9 kb) fragment. Furthermore, the next sexual progeny of the regenerants which had a three-fragment pattern further segregated into three- and two-fragment patterns.These results, in conjunction with previous reports on Nor region variability among tissue-culture derived plants, suggest that this variability is not invariably related to in vitro culture.

Genetic variation in an inbred plant: variation in tissue cultures of soybean [Glycine max (L.) Merrill

Although soybean [Glycine max (L.) Merrill] grows as an inbreeding, generally homozygous, plant, the germplasm of the species contains large amounts of genetic variation. Analysis of soybean DNA has indicated that variation of RFLP (restriction fragment length polymorphism) markers within the species usually entails only two alleles at any one locus and that mixtures of such dimorphic loci account for virtually all of the restriction fragment variation seen in soybean (G. max), and in its ancestors, G. soja and G. gracilis. We report here that tissue cultures prepared from root tissue of individual soybean plants develop RFLP allelic differences at various loci. However, these newly generated alleles are almost always the same as ones previously found and characterized in other varieties of cultivated soybean (cultivars). This repeated generation of particular alleles suggests that much of the genetic variation seen in soybean could be the consequence of specific, relatively frequently employed, recombinational events. Such a mechanism would allow inbred cultivars to generate genetic variation (in the form of alternative alleles) in a controlled manner, perhaps in response to stress.

‘Redlander’ Tomato

Abstract Susceptible tomato (Lycopersicon esculentum Mill.) cultivars in coastal Queensland may suffer substantial losses from bacterial wilt [Pseudomonas solanacearum (Smith 1896) Smith 1914 biovar III] from late spring to autumn (3). Verticillium wilt (Verticillium dahliae Kleb. race 1) can be a major disease from autumn to early spring. A hybrid cultivar, Redlands Summertaste (1), recently was released and is resistant to bacterial wilt, verticillium wilt, and fusarium wilt [Fusarium oxysporum Schlecht, f.sp. lycopersici (Sacc.) Snyder &amp; Hansen race 1 and 2]. However, although this cultivar has high yields (75 to 92 t·ha–1), the jointed fruit attachment and indeterminate growth habit limit returns to growers who have high labor costs. ‘Redlander’ was developed as an inbred cultivar to provide a locally adapted tomato in which resistances to bacterial, verticillium, and fusarium wilts are combined with good fruit quality, jointless pedicel, and determinate growth habit.

Response of Ten Corn Cultivars to Flooding

ABSTRACT EMERGENCE, growth and mineral uptake of five inbred and five hybrid corn cultivars when flooded for 0, 2, 4 or 6 days at the pregermination and the 4-5 leaf seedling growth stages was determined. Emergence following pregermination flooding was determined under laboratory and field conditions at cold and warm temperatures during flooding. Growth and mineral uptake were determined for seedlings growing in the field and flooded at warm temperatures. Emergence percentage decreased as flooding duration and temperature increased during flooding. Dry matter per plant was reduced as flooding duration increased. Hybrid cultivars were more susceptible to flooding than inbred cultivars at both growth stages. The concentration of N, P, Ca, Mg and Cu in the plant decreased while Fe, Al, and Na increased with increased flooding. Potassium concentration peaked at 2 days of flooding then decreased, while Mn and Zn showed a reversed trend