Benjavan Rerkasem

Genotypic variation in plant response to low boron and implications for plant breeding

Plant response to low B in the soil varies widely among species, and among genotypes within a species. Boron efficient genotypes are those that are able to grow well in soils in which other genotypes are adversely affected by B deficiency. This review considers the extent of variation in B efficiency in plant species and genotypes, the physiological nature of the efficiency mechanisms, what is known of the genetic basis for inheritance, screening techniques and the practical implications of the genotypic variations.Frequently, B efficiency is the sole reason for a difference between an average yield and complete crop failure. Severe yield losses can be effectively prevented by the inclusion of B efficiency as a selection criterion in crop breeding and improvement programmes for regions with low B soils. In addition, the expression of B deficiency primarily through male sterility, which is common in many species, creates opportunities for outcrossing in normally self-fertilised species. This, in turn, leads to two possibilities. Firstly, self fertilisation, and therefore maintenance of pure lines, cannot always be assumed in self pollinated species where B efficient and inefficient genotypes are grown side by side on low B soils. Secondly, B deficiency, in soil or artificial media, may be used as a fertility selective medium in which the male sterile B inefficient genotypes and the male fertile B efficient genotypes could hybridise naturally. This would be useful as a simple and economical method for creating heterozygous populations in breeding programmes as well as for producing hybrid seeds. Now that the roles of B in plant growth and development are beginning to be clarified, the efficiency mechanisms as well as the governing genetics can be explained. Practical benefits from the genetic diversity of B efficiency will be enhanced by a better understanding of B efficiency mechanisms and the molecular bases for their genetic control.

Boron in plant and animal nutrition

This book comprises the contributions of the international workshop Boron 2001 which was aimed at gathering all relevant information on recent developments in boron research in soils, plants, animal and men over the past years. Review articles and original contributions deal with both applied and basic aspects in this area, comprising topics such as methods for B determination, the physiological functions of boron in plant and animal metabolism, including use of 10B for diagnostic purposes and cancer treatment. Genetic and molecular aspects of boron efficiency and tolerance to toxic levels in plants and the early physiological reactions to boron deprivation are further important topics of this volume. The role of boron for reproductive development is dealt with in further contributions. Furthermore, improved methods for the diagnosis of the available boron status in soils, plants appropriate timing and leaf fertilizer application are addressed. Special emphasis is given in the contributions to highlight the most recent developments in the aforementioned areas.

Boron in Soils and Plants

Boron (B) deficiency problems for crop production have been identified recently in Bangladesh. Information on the subject is still limited. Deficiency symptoms typical of B have been observed in a wide range of crops including: deformed and poor root growth; death of plant apices; failure in seed setting; abortion of flowers; thick pod walls with small or no seeds; discolouration of vegetables. Deficiency of B in plants has been considered responsible for causing sterility in wheat, and mustard in the country, although it was recently reported that low soil B is not the sole factor inducing wheat sterility. The available B level in major soil types of Bangladesh ranged between 0.1 to 1.9 mg kg1 soil. Non-calcareous grey floodplain soil (Typic Fluvaquent), Terrace soil (Typic Haplaquept) and Hill soil (Lithic Udorthent), which are the principal light textured acid soils generally contain low levels of available B (0.1-0.3 mg kg-I). Approximately 1 million ha of cultivable land may have B deficiency problems. Yield increases to the extent of 10-92% by B fertilization in wheat and 14-52% in different vegetables were recorded from several field trials in B deficient areas in the northern zones of Bangladesh. A sharp decline in B availability in soil is expected to occur in the near future due to both crop intensification and crop diversification as Bangladesh strives for increased agricultural production. Hence B demands more attention, along with better crop management practices, in the context of sustainable agricultural production.

Measurement of N2 fixation in maize (Zea mays L.)—ricebean (Vigna umbellata [Thunb.] Ohwi and Ohashi) intercrops

The yield of N in maize (Zea mays L.) and ricebean (Vigna umbellata [Thumb.] Ohwi and Ohashi) were compared on a Tropoqualf soil in North Thailand in 1984 and 1985. Both species were grown in field plots in monoculture or as intercrops at a constant planting density equivalent to 8 maize or 16 ricebean plants per m2. The contribution of symbiotic N2 fixation to ricebean growth was estimated from measurements of the natural abundance of15N (δ15N) in shoot nitrogen and from analysis of ureides in xylem sap vacuumextracted from detached stems.The natural abundance of15N in the intercropped ricebean was found to be considerably less than that in monoculture in both growing seasons. Using maize and a weed (Ageratum conyzoides L.) as non-fixing15N reference plants the proportions (P15N) of ricebean shoot N derived from N2 fixation ranged from 0.27 to 0.36 in monoculture ricebean up to 0.86 when grown in a 75% maize: 25% ricebean intercrop. When glasshouse-derived calibration curves were used to calculate plant proportional N2 fixation (Pur) from the relative ureide contents of field collected xylem exudates, the contribution of N2 fixation to ricebean N yields throughout the 1985 growing season were greater in intercrop than in monocrop even at the lowest maize:legume ratio (25∶75). Seasonal patterns of sap ureide abundance indicated that N2 fixation was greatest at the time of ricebean podset. The averagePur andP15N in ricebean during the first 90 days of growth showed identical rankings of monocrop and intercrop treatments in terms of N2 fixation, although the two sets ofP values were different. Nonetheless, seasonal estimates of N2 fixation during the entire 147 days of legume growth determined from ureide analyses indicated that equivalent amounts of N could be fixed by ricebean in a 75∶25 intercrop and in monoculture despite the former being planted at one-quarter the density.

Effects of Boron on Pollen Viability in Wheat

Grain set failure in wheat, caused by boron (B) deficiency, is associated with poorly developed pollen and anthers. This paper presents results of a study of the effect of B on pollen viability when it was supplied “internally” through the roots and externally in an agar medium for in vitro germination. There was no major effect of B supply to wheat plants on the number of pollen anther−1 or the percentage of pollen with positive reaction to iodine. Pollen germination in the medium was, however, responsive to both internal and external B supply. When B was not added to the medium, germination was poor, regardless of the level of B supplied to the plant, in both a B deficiency sensitive (SW41) and a B deficiency tolerant (Sonora 64) genotypes. The percentage of germinated pollen and length of the pollen tube increased with increasing medium B. With 20-100 mg H3BO3 L−1 in the medium, the percentage of germinated pollen and length of the pollen tube responded positively to increasing B supply to the plant.

Nitrogen Fertilizer Increases Seed Protein and Milling Quality of Rice

ABSTRACT Rice grain breakage during milling is a problem in many parts of Asia. It has been suggested that nitrogen (N) fertilizer can improve the milling quality of rice. Therefore, this study investigates effects of N fertilization on grain N concentration, endosperm storage protein distribution, and milling quality of rice. Four Thai extra long grain commercial rice cultivars (KDML105, KLG1, PTT1, and CNT1) were grown at Chiang Mai University in the wet season of 2001 with 0 or 120 kg of N/ha at flowering. Anatomical sections showed that there was more storage protein accumulated in the lateral regions of polished grain of high N concentration than in grain of low N concentration. Percent (%) unbroken rice was positively correlated with relative abundance of storage protein in the lateral region of the endosperm in all cultivars. Applying N increased head rice N concentration in all cultivars, whereas % unbroken rice was increased in KLG1 and CNT1. KDML105 cultivar, on the other hand, already had high ...

Boron deficiency induced male sterility in wheat (Triticum aestivum L.) and implications for plant breeding

Boron (B) deficiency causes grain set in wheat to fail. A wide range of genotypic variation in the response to low B has been observed. Genotypes were screened in low B in soil and sand culture, and classified into five groups, namely, very sensitive, sensitive, moderately sensitive, moderately tolerant and tolerant. At very low levels of B, the very sensitive to sensitive genotypes were completely male sterile and set only a few or no grain, while the tolerant genotypes set grain normally. Natural outcrossing was detected in these male sterile plants when a tolerant genotype was growing nearby. Grain set by cross fertilisation was markedly enhanced by a B application directly on the ear of the male sterile plants. Three practical implications are suggested. Firstly, genotypes that are tolerant to low B can provide a solution for grain set failure caused by B deficiency. Secondly, the potential for outcrossing in male sterile B deficient wheat has to be taken into account in the maintenance of pure lines in low B soils even though wheat is normally self pollinated. Thirdly, a simple and novel method for hybridization is suggested, in which B deficiency is used as fertility selective medium and male sterile female parents and fertile male parents are provided by genotypic variation in the response to low B.

Grain set failure in boron deficient wheat

Effects of boron (B) deficiency on reproductive development and grain set in wheat was studied in experiments in a sand culture in which grain set was increased by increasing B supply in the nutrient solution. Early vegetative response was also studied in a solution culture experiment with 5 μM B and without added B. Effects of B deficiency on the male and female part of the wheat flower were studied in a cross fertilization experiment involving B deficient and B sufficient wheat plants. An international trial (the Boron Probe Nursery) was conducted as a collaboration between Chiang Mai University, CIMMYT and National Agricultural Research Systems in various countries, to verify the B response in non-traditional, warm wheat-growing areas.

THE EFFECT OF N FERTILIZER STRATEGY ON N2 FIXATION GROWTH AND YIELD OF VEGETABLE SOYBEAN

Abstract Vegetable soybean ( Glycine max ) is a lucrative cash crop predominantly grown in Japan, Taiwan, China, Thailand, and Vietnam. Although soybean has the capacity to satisfy a large proportion of its own nitrogen (N) requirements via N 2 fixation, farmers are recommended to apply several side-dressings of fertilizer N during growth in the belief that this will maximize pod yield. A field experiment was conducted in northern Thailand to evaluate the effect of six different N fertilizer management strategies on crop growth and marketable pod yield of vegetable soybean and to assess the impact of fertilization on the potential carry-over of residual fixed N remaining after harvest. A vegetable soybean crop was supplied with 25 kg N ha −1 ammonium sulphate as starter N at sowing, then areas of the crop either received no further fertilizer N, or received one (50 kg N ha −1 ), or two (50 + 25 kg N ha −1 ) urea top-dressings at different stages of vegetative and/or reproductive growth. The field trial demonstrated that the appropriate timing of N fertilization could improve both crop growth and pod yield. Crop biomass was increased by 11 to 16% and pod yield improved by up to 44% if starter N was followed by a single top-dressing at either early vegetative growth or at flowering. However, there was no additional benefit from the standard farmer practice of supplying two top-dressings prior to flowering. However, if an early vegetative application of fertilizer N was followed by a second dressing either during flowering or pod-fill a further 20% increase in marketable pod yield was achieved. The effect of fertilizer N on soybeans capacity to fix N was complex. The proportion of plant N derived from N 2 fixation (Pfix) was highest when only starter N 2 was applied (seasonal average of 84% of crop N 2 coming from N 2 fixation). Any further top-dressing with N-fertilizer depressed nodulation and Pfix, but also increased crop growth so that amounts of N, fixed were similar for most fertilizer treatments (adjusted to account for below-ground N: 149 to 153 kg N ha −1 cf 147 kg N ha −1 fixed in the presence of starter N alone). However, N 2 fixation was significantly depressed by the farmer practice of top-dressing N twice before flowering (117 kg fixed N ha −1 , and was highest when fertilizer N was supplied during a period of peak N demand at pod filling (180 kg N ha −1 ). Between 53 and 92 kg N ha −1 was removed from the crop in marketable pods. But since N 2 fixation remained the dominant N source for crop growth in all treatments, substantial amounts of fixed N (64 to 91 kg of fixed N ha −1 were estimated to remain in leaf, stem and root residues after harvest. However, the potential N benefit from including vegetable soybean in a cropping sequence disappeared if the above-ground residues were removed from the field as is the common practice in many Asian farming systems.

Boron requirement for reproductive development in wheat

The effect of boron (B) deficiency on reproductive development was examined in a wheat line SW41 at 4 B levels in a field experiment. The soil B levels (designated BO, B1, B2, B3) ranged from 0.1 to 0.2 mg hot water soluble B kg-1. No effect on vegetative growth was detected at any of the B levels, but the number of grains per ear increased with B, from 7 in BO to 21 in B3; and Grain Set Index (GSI) also increased from 22 to 60%. At ear emergence, B content (mg B kg-1 DW) of the ear ranged from 2.2 to 3.1, and of the flag leaf from 4.1 to 4.7, but these bore slight to no relationship to the number of grains per ear or GSI. Higher B concentrations were found in the carpel, and higher still in the anthers. More significantly, grain set was closely correlated with B in the carpel (R2 = 0.86) and anthers (R2 = 0.77). The significant correlation between GSI and carpel and anther B was confirmed with a larger set of data. With 7 mg B kg-1 DW in the anthers and 5 mg B kg-1 DW in the carpel, the number of grains per ear was doubled when cross pollination with B deficiency tolerant Fang 60 growing near by was allowed. In ears with 9 mg B kg-1 in the anthers and 8 mg B kg-1 in the carpel the effect of cross pollination was smaller, but still significant. The critical deficiency concentration (CDC) of B for the anthers was determined at 10 mg B kg-1 and for the carpel at 8 mg B kg-1.