Crop Breeding in the Twenty-First Century

SUMMARY

One can predict a future in which professional plant breeding, especially in the private sector, will be significantly scaled back, and advanced biotechnologies (e.g., genetic engineering) will be forbidden for use in plant breeding. Alternatively, one can predict a future in which commercialism will rule all sectors. But a more optimistic outlook predicts that the current tripartite division of responsibilities will prevail: Private Sector, Public Sector, and Participatory (i.e., farmer-breeder partnerships). The global plant breeding system is composed of separate organs, each essential for the survival of the whole but each with a different function. All parts work together for the good of the whole.     

Application of Molecular Markers in Breeding for Nitrogen Use Efficiency

Summary

Nitrogen use efficiency (NUE) is defined as dry matter yield produced per unit of N supplied and available in the soil. NUE is approximately 33% for cereal production worldwide. Increased cereal NUE must accompany increased yield needed to feed the growing world population. Consequently, continued efforts are needed to include plant selection under low N input which is not often considered a priority by plant breeders. Molecular markers have accelerated plant breeding in a number of areas including biotic (disease and insect) resistance and abiotic (drought, low nitrogen fertilization and frost) tolerance. Marker-based technology has already provided scientists with a powerful approach for identifying and mapping quantitative trait loci (QTL) and would lead to the development of a better understanding of genetic phenomena. Two main NUE studies have been discussed. The first study identified QTL for NUE in maize involved the grain yield and secondary morphological traits of interest, such as plant height, ear leaf area, ears per plant and kernels per ear. This was compared with second study of QTL for yield and its components with genes encoding cytolistic gult-amine synthestase and leaf N0₃ ^- content. These secondary traits were correlated with yield and demonstrated segregation with high heritability under low nitrogen conditions. Marker assisted selection (MAS) should be able to offer significant advantages in cases where phenotypic screening is particularly expensive or difficult, including breeding projects involving multiple genes, recessive genes, late expression of the trait of interest, seasonal considerations, or geographical considerations. In addition to reducing costs of conventional breeding, MAS also has the potential to generate time savings. Possibly, the greatest contribution of QTL mapping to plant breeding will be the basic understanding of the genetic architecture of quantitative traits, thereby relating specific genetic loci with the biological mechanisms associated with desirable phenotypes.     

Germplasm Enhancement and Breeding Strategies for Crop Quality in Japan

Abstract

Rice is the staple food for most Asians. Breeding efforts at the national and international levels have resulted in high-yielding varieties with resistance/tolerance to biotic and abiotic constraints. Consequently Asia has enjoyed rice self-sufficiency in recent years. Now in some countries over-production of rice has occurred, partly because of reduced rice consumption. For instance, in 1962 Japan had a per capita rice consumption of 118.3 kg and then this rapidly declined to about 60kg in 2003. Imbalances between production and consumption in rice and other crops have promoted a paradigm shift of breeding objectives oriented from producers to consumers. Germplasm enhancement (pre-breeding) and breeding strategies now focus on a broad range of crop and food qualities, which are closely associated with industrial and processing properties and human health and nutrition. In particular, physiological functions of chemical compounds involved in crop products are being studied as a part of breeding programs. Diverse plant genetic resources and advances in plant genome research have contributed to successful breeding strategies to improve and manage crop and food quality. Recent progress in germplasm enhancement and breeding strategies for quality improvement of rice, wheat, soybean and sweet potato in Japan is discussed.     

Increasing Crop Competitiveness to Weeds Through Crop Breeding

Abstract

Increasing the ability of crops to compete against weeds, through either enhancing crop tolerance or crop interference to weeds, provides an attractive addition to current weed control practices and could be an integral component of weed management systems. Research has shown that considerable variability exists among crop culti-vars with respect to their ability to compete with weeds. Despite this evidence, directed research on competitive crops has been minimal. Reasons for this lack of emphasis in plant breeding programs include the effectiveness of current weed management with tillage and herbicides, and the lack of easily identifiable crop characteristics that are indicative of weed competitiveness. Expanded knowledge of specific crop-weed interactions would facilitate crop competitiveness to weeds through either crop management practices or plant breeding. Plant breeders need basic and applied information to identify favorable crop-weed competitive traits in order to enhance or incorporate those traits into crop cultivars. Accelerated research on weed competitive crops should lead to more economical, effective, and feasible integrated weed management programs for all crops.     

Metabolie Engineering of Flower Color in Ornamental Plants

Abstract

Advances in the knowledge of plant pigment pathways at genetic, biochemical and molecular levels, and the establishment of genetic transformation methods for an increasing number of plant species have paved the way to genetic engineering of flower and plant color for ornamental purposes. From trial-and-error approaches based on the available few genes, the trend is now to comprehensively study the target species, genotypes and pigment pathways to precisely address specific breeding goals. This review examines the state of the art in this field, from the pioneering stages to fundamental and applied research on flavonoids, which is being extended to carotenoids and is also likely to involve other pigments in the near future.     

Genetic gain of Al tolerance and contribution of agronomic traits on Al tolerance in the early stage of sorghum breeding program

ABSTRACT

Genetic gain (GG), heritability and contribution of the agronomic traits on Al tolerance are precious information for selection strategy in the breeding of Al-tolerant sorghum. The objectives of this study were (i) to estimate the GG of Al tolerance in sorghum and (ii) to determine the direct effect of agronomic traits on Al tolerance through path analysis. Evaluation of agronomic characters used F₂, and F₃ sorghum progenies in field experiment and screening of Al tolerance used the hematoxylin-staining method. Three sorghum populations showed the low GG of Al tolerance (GG = 0.558–1.108). This result indicates that high allocation of progenies in the early stages of the Al-tolerant breeding program and high selection differential (sd) of Al tolerance should be applied to obtain a higher gain of Al tolerance. Selection pressure for early maturity (sd = ?2.942) and short plant height (PH) (sd = ?38.165) resulted in lower improvement of GG for Al tolerance. The high dry weight and tall PH provided a more genetic contribution to the advancement of Al tolerance. Based on the overall path analysis data, the increase of plant biomass, the significant number of progenies in the early stage of breeding and strong sd of Al tolerance would be more appropriate to improve the Al tolerance in sorghum.     

Food-Based Approaches for Alleviating Micronutrient Malnutrition: An Overview

SUMMARY

This chapter reviews current knowledge and experience with using food-based approaches in reducing vitamin A and iron deficiencies. It reviews recently published literature, highlights some lessons learned, and identifies knowledge gaps and research priorities. The main strategies reviewed are food-based interventions that aim at: (1) increasing the production, availability, and access to vitamin A and iron-rich foods through the promotion of home production and (2) plant breeding strategies that have the potential to increase the content of vitamin A and iron in diet as well as their bioavailability. The review highlights the fact that significant progress has been achieved in the past few decades in the design and implementation of food-based approaches. Evaluations however remain weak, and without rigorous, carefully conducted evaluations the real potential of food-based approaches in addressing micronutrient malnutrition cannot be fully understood. Plant breeding strategies, although they are at a much earlier stage of development, hold great promise because of their enormous potential to improve the dietary quality of populations relying mainly on cereal staples. Studies on human bioavailability are the next crucial step to help understand the potential contribution of plant breeding towards alleviating micronutrient malnutrition. Our review suggests that food-based interventions could be an essential part of the long-term global strategy for the fight against micronutrient malnutrition, but their real potential is still to be explored.     

Molecular Breeding for Rainfed Lowland Rice in the Mekong Region

Abstract

In the past 20 years, the rice-breeding program in Thailand had little success in developing new cultivars to replace Kao Dawk Mali 105 (KDML105) and Kao Khor 6 (RD6) for the rainfed lowland rice environments. The main reason for the poor adoption of new cultivars by farmers is the susceptibility to diseases and unacceptable grain qualities. The conventional breeding program also takes at least 15 years from initial crossing to the release of new cultivars. A new breeding strategy can be established to shorten the period for cultivar improvement by using marker-assisted selection (MAS), rapid generations advance (RGA), and early generation testing in multi-locations for grain yield and qualities. Four generation of MAS backcross breeding were conducted to transfer genes and QTL for bacterial blight resistance (BLB), submergence tolerance (SUB), brown plant hopper resistance (BPH) and blast resistance (BL) into KDML105. Selected backcross lines, introgressed with target gene/QTL, were tolerant to SUB and resistant to BLB, BPH and BL. The agronomic performance and grain quality of these lines were as good as or better than KDML105.     

Four Decades of Breeding for Varietal Improvement of Irrigated Lowland Rice in the International Rice Research Institute

Abstract

Since the establishment of the International Rice Research Institute (IRRI) in 1960, IRRI’s breeding effort in varietal improvement for irrigated lowland has passed four decades. Breeding of semi-dwarf rice varieties such as IR8 at IRRI during first decade from 1960 to 1969 resulted in quantum leaps in yield potential, which marked the green revolution in Asia. During the second decade from 1970 to 1979, the primary emphasis of rice improvement has been directed towards incorporation of multiple disease and insect resistance and shortening of growth duration. Grain quality was the main target of crop improvement at IRRI during the third decade from 1980 to 1989. The fourth decade from 1990 to 1999 and beyond was focused again on the improvement of yield potential by developing hybrid rice and new plant type. Up to 1999, 46 indica inbred varieties and 2 indica/indica hybrid rice varieties were developed by IRRI and released in the Philippines for the irrigated lowland rice systems. Large-scale adoption of these improved varieties under modern crop management practices has resulted in a dramatic increase in rice production in major rice-growing countries. The hybrid varieties between indicas increased yield potential by 9% under the tropical conditions. New plant type (NPT) breeding has not yet resulted in an increase in yield potential. The second generation NPT developed by crossing tropical japonica with indica has demonstrated some promising results in terms of improvements in yield potential, disease and insect resistance, and grain quality.     

Characterization of Aroma and Agronomic Traits in Afghan Native Rice Cultivars

Abstract

In this study, we collected native aromatic rice cultivars from north, east and northeast of Afghanistan, and check cultivars from Japan, Thailand and India. We characterized some important agronomic characters such as plant height, panicle number per plant, grain number per panicle, 1,000-grain weight, grain length and grain width to find the desirable characters for breeding programs. Many of them were classified into tall culm rice according to IRRI index, but had thin and slender grain, and strong aroma which are favorable characteristics in Afghanistan and surrounding regions. The aromatic character was characterized by three methods, 1.7% KOH sensory test, gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM), and polymerase chain reaction (PCR) analysis. These three methods gave similar results. Six out of 10 Afghan native rice cultivars were aromatic and four non-aromatic. Among the check cultivars, Basmati 370, Jasmine 85, Izayoi, Oitakoutou and Jakouine were aromatic and Nipponbare non-aromatic. Improvement of aromatic and high yielding rice and reduction of plant height are the important objectives for rice breeding in Afghanistan. The results showed that Pashadi Konar from Afghanistan has the intermediate plant height, heavier 1,000-grain weight (32 g), longer grain (11 mm) and favorable aroma. Therefore, this cultivar may be a good source of aromatic rice germplasm in Afghanistan. To clarify the genetic nature of aroma in rice, we crossed non-aromatic cultivar Nipponbare with aromatic cultivar Jasmine 85, and examined the aromatic character in the F₂ generation by 1.7% KOH sensory test and PCR analysis. Non-aromatic and aromatic characters were segregated at a ratio of 3:1, showing that aroma is controlled by a single recessive gene.     

Emergence and plant stand of pregerminated true potato seed in warm climate

Pregermination of true potato seeds obtained from open pollination of breeding lines and F₁, hybrids improved the emergence and stand in a warm climate. Considerable differences in emergence existed within the breeding lines and F₁ hybrids. With proper selection of breeding lines and pregermination of seeds, it would be possible to obtain a desirable plant stand in a warm climate.     

Genotype–Environment Interactions of Selected Rice Lines in Direct Water-Seeded Culture

Summary

Five rice genotypes including 4 breeding lines (lines 36 and 42 from the cross of Aoinokaze//Lemont/ Hinohikari and 53 and 76 from Yumehikari//Lemont/Hinohikari) and a reference cultivar, Hinohikari, were grown under various environmental conditions (year, location, plant density and nitrogen level) to determine the genotype-environment interactions for yield, yield components and yield adaptability in water direct-seeded culture. No genotype-year interactions were found in yield or yield components, i.e., the ranking of the genotypes did not change across the years. The interactions of genotype with plant density and nitrogen level were significant only in the percentage of filled grains, indicating that the ranking of rice genotypes for yield traits except the percentage of filled grains remained constant across plant densities and nitrogen levels. There were significant differences in the ranking in grain yield of genotypes between the plants cultivated in Fukuoka and Chikushino. However, line 42 was ranked the highest at both locations. The adaptability to environmental conditions evaluated by a regression method varied with the genotype and line 42 which showed high average yield and higher yield in high-yielding conditions was selected to be suitable for direct-seeded culture.     

Transgenic Approaches to Disease Resistance in Ornamental Crops

Abstract

Viral, bacterial, and fungal diseases of ornamental plants cause major losses in productivity and quality. Chemical methods are available for control of fungal diseases, and to a lesser extent for bacterial diseases, but there are no economically effective chemical controls for viral diseases except to control vector species. Host plant resistance is an effective means of controlling plant diseases, and minimizing the necessity for the application of pesticides; however, there are many ornamentals in which no natural disease resistance is available. It is possible to introduce resistance derived from other species, or even from the pathogen itself, by genetic engineering. This allows the introduction of specific, or in some instances broad spectrum, disease resistance into plant genotypes that have been selected for desirable horticultural characters; in contrast, introduction of natural resistance by traditional breeding may take many cycles of breeding to combine disease resistance with desirable ornamental quality. This article briefly reviews existing work on transformation systems for ornamentals, and discusses the various approaches to introducing resistance to viral, bacterial, and fungal diseases, and to nematode infestations. These include pathogen-related proteins, R genes, and general pathogen resistance; anti-microbial peptides; expression of anti-pathogen antibodies; viral sequences; ribozymes; antiviral peptides; ribonucleases; and ribosome-inactivating proteins. Examples are given of application of these approaches to disease resistance in other types of crop and model plant systems, and actual or potential application to disease resistance in ornamentals. Future prospects for obtaining plants with multiple pest and disease resistances are discussed.     

Sorghum Diversity Evaluated by Simple Sequence Repeat (SSR) Markers and Phenotypic Performance

Abstract

Analysis of phenotypic performance in the field in combination with molecular analysis provides useful information to increase the efficiency in plant breeding programs. We investigated: (i) the relationship between phenotypic performance and genetic diversity determined using simple sequence repeat (SSR) markers, (ii) the possibility of grouping inbred lines based on phenotypic performances and (iii) the genotypic and phenotypic variance of yield, yield components and primary agronomic traits among inbred lines. Among 22 sorghum inbred lines, grain yield per plot and days to flowering were less representative as phenotypic markers. However, the following six phenotypic traits showed high heritability; 1000-grain weight, ear length, plant height, stalk diameter, dry weight and harvest index, and were useful as phenotypic markers. The data obtained using SSR markers significantly correlated with those of phenotypic performance in this study, and the grouping of inbred lines based on the combination of the performance of six phenotypes was similar to that based on SSR markers. On the basis of phenotypic performance, four inbred lines, D12, H11, C9xH13 and C9xH11, were selected as promising parents for plant breeding programs.     

Susceptibility of potato varieties and advanced breeding lines (Solanum tuberosum L.) toPhytophthora infestans (Mont.) de Bary in greenhouse screenings

Late blight (Phytophthora infestons (Mont.) de Bary) has re-emerged as an important pathogen of the cultivated potato (Solanum tuberosum subsp.tubero-sum L.) in North America. The purpose of this study was to evaluate the relative susceptibility of potato germplasm in the greenhouse in order to initiate a breeding program for resistance to the US-8/A2 mating type which is the more aggressive and prevalent strain of late blight. Whole plants of 147 cultivars and breeding lines were evaluated. Percent plant area infection was visually assessed. Seven days after inoculation, infection ranged from 0 to 100% and the overall mean was greater than 50%. Two-thirds of the cultivars and breeding lines tested were very susceptible to the US-8 genotype. The highest resistance was identified in the somatic hybrids betweenS. tuberosum andS. bulbocastanum and their backcross derivatives. Pike and Snowden were less susceptible than the other North American cultivars. Zarevo was most resistant among the European cultivars. Seven of the advanced breeding lines were equivalent to Zarevo in infection levels. The host plant resistance identified among the material tested in this study can be used by breeding programs to develop improved cultivars with resistance to US-8 genotypes of late blight.     

A Simple and Low-Cost Method to Classify Amylose Content of Rice Using a Standard Color Chart

Abstract

An alternative method to classify amylose content in rice was developed. In this method, based on amylose-iodine colorimetry, a standard color chart was used instead of a spectrophotometer to successfully classify a wide range of cultivars with known and unknown amylose content. This is a rapid low-cost method that may be useful for prediction of amylose content in rice for breeding purposes.     

Analysis of Genotype-by-Environment Interaction for Agronomic Traits of Durum Wheat in Iran

Abstract

Grain yield of durum wheat (Triticum turgidum L. var. durum) under Mediterranean conditions is frequently limited by both high temperature and drought during grain filling. Genotype-by-environment (GE) interaction and genotype-by-trait (GT) data were analyzed for agronomic performance of durum wheat breeding lines. Data were obtained from 18 durum wheat breeding lines and two cultivar checks (Zardak and Sardari) for their agronomic performance under three different climate locations (moderate, warm and cold winters) and two moisture regimes (rainfed and two supplemental irrigations conditions) in two cropping seasons (2006 and 2007) in Iran. Analysis of GE interaction data based on multiple traits showed that the environment (combination of year-location- moisture regimes) effect was always the most important source of trait variation, accounting for 58.6 to 98.4% of the total variation. Biplot analysis of the studied traits revealed that (i) the locations tended to discriminate genotypes in dissimilar fashions, and (ii) the relationships among traits were not consistent over the locations, where they facilitated visual genotype comparisons and selection at each location.     

Non-destructive shoot biomass evaluation using a handheld NDVI sensor for field-grown staking Yam (Dioscorea rotundata Poir.)

ABSTRACT

Crop phenotyping is a key process used to accelerate breeding programs in the era of high-throughput genotyping. However, most rapid phenotyping methods developed to date have focused on major cereals or legumes, and their application to minor crops has been delayed. In this study, we developed a non-destructive method to predict shoot biomass by measuring spectral reflectance in staking yam (Dioscorea rotundata). The normalized difference vegetation index (NDVI) was evaluated using a handheld sensor that was vertically scanned from the top to the bottom of a plant alongside the stake. A linear regression model was constructed to predict shoot biomass through Bayesian analysis using NDVI as a parameter. The model well predicted the observed values of shoot biomass, irrespective of the growth stage and genotypes. Conversely, the model tended to underestimate the shoot biomass when the actual shoot biomass exceeded 150 g plant^?1; this was compensated for when the parameter green area, calculated from plant image, was included in the model. This method reduced the time, cost, effort, and field space needed for shoot biomass evaluation compared with that needed for the sampling method, enabling shoot biomass phenotyping for a large population of plants. A total of 210 cross-populated plants were evaluated, and a correlation analysis was performed between the predicted shoot biomass and tuber yield. In addition to the prediction of tuber yield, this method could also be applied for the evaluation of crop models and stress tolerance, as well as for genetic analyses.     

Stability analysis of seven agronomic traits for soybean [(Glycine max (L.) Merr.] Tokachi nagaha and its derived cultivars using the AMMI model

The stabilities of seven agronomic traits were analyzed and the general stabilities of soybean [Glycine max (L.) Merr.] accessions were evaluated based on the additive main effects and multiplicative interactions (AMMI) model using the founder parent Tokachi nagaha and 137 of its derived cultivars as materials. The objective was to provide a theoretical basis for effectively using germplasm in soybean breeding and production. Analysis of variance (ANOVA) showed that genotype, environment, and genotype by environment interactions were significantly different for each trait. The first three interaction principal components axes (IPCA) were highly significant, accounting for 61.28–70.00% of the total variation. The stability differed for the different traits. 50 cultivars with high general stabilities were identified. The general stability of Tokachi nagaha was moderate, as the stability coefficients (D_i) of its seven traits were relatively high; this must be considered by breeders using this cultivar as a breeding parent. There were significant positive correlations between the phenotypic values and their own D_i values for number of branches per plant, number of pods per plant, number of seeds per plant, and seed weight per plant. This would lead to the expectation that the phenotypic stability would be lower when a cultivar had more branches, pods, seeds, and high per plant yields. Thus, it appears difficult to breed cultivars that simultaneously have high yields and high stability.     

Ammonia Emission from Leaves of Different Rice (Oryza sativa L.) Cultivars

Abstract

NH₃ emission from leaves of three rice (Oryza sativa L.) cultivars, Akenohoshi, Shirobeniya and Kasalath, was examined using a simple open chamber system.　In the three cultivars, NH₃ emission rate (AER) and NH₄⁺ content of leaves decreased with decreasing NH₄⁺ concentration in the root medium, but these values differed significantly with the cultivar. In the daytime, AER, NH₄⁺ content and glutamine synthetase (GS) activity in leaves changed similarly with maximum values around midday. Akenohoshi showed significantly lower AER and NH₄⁺ content but higher GS activity than Kasalath. The difference in AER among the rice cultivars may be related to the activity of GS involved in photorespiratory NH₃ recycling. Akenohoshi can be a breeding material useful for improving N recycling.