Boron deficiency in maize

Boron (B) deficiency depresses wheat, barley and triticale yield through male sterility. On the basis of field responses to B fertilization, maize (Zea mays L.) is affected by B deficiency in five continents. In a series of sand culture trials with maize subject to B0 (nil added B) and B20 (20???M added B) treatments, we described how B deficiency depressed maize grain yield while showing an imperceptible effect on vegetative dry weight. With manual application of pollen to the silk of each plant, B0 plants produced 0.4 grain ear^?1 compared with 410 grains ear^?1 in B20 plants. Symptoms of B deficiency was observed only in B0 plants, which exhibited symptoms of narrow white to transparent lengthwise streaks on leaves, multiple but small and abnormal ears with very short silk, small tassels with some branches emerging dead, and small, shrivelled anthers devoid of pollen. Tassels, silk and pollen of B0 plants contained only 3?C4?mg B kg^?1 DW compared with twice or more B in these reproductive tissues in B20 plants. A cross-fertilization experiment showed that, although the tassels and pollen were more affected, the silk was more sensitive to B deficiency. Pollen from B20 plants applied to B0 silk produced almost no grains, while pollen from B0 on B20 silk increased the number of grains to 37% of the 452 grains plant^?1 produced from B20 pollen on B20 silk. Therefore, the silk of the first ear may be targeted for precise diagnosis of B status at maize reproduction, for timely correction by foliar B application, and even for B-efficient genotype selection.     

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 M 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.There was a wide genotypic variation in reproductive responses to B among the eight wheat genotypes studied. In sand culture with low B (0.2 M), grain set index ranged from 9.5% in SW41 to 94.5% in Fang 60; with high B (10 M) it was 90% in all genotypes. Early vegetative response to B was measured in the length of the youngest emerged blade at 12 days after sowing. Without added B the length of the leaf blade relative to that with 5 M B ranged from 0.82 to 0.92. This indicates some variation in vegetative response to B among the genotpes. However, there was no relationship between vegetative and reproductive responses to B of the wheat genotypes.Fertility of both the male and female part of the wheat flower appears to be affected by B deficiency. Ears from B deficient plants that were bagged to prevent cross fertilization set no grain. Cross pollination of B deficient female flowers with pollen from B sufficient plants resulted in only 28% grain set, compared with 94% percent from manual crossing of B sufficient pollen on B sufficient female.Reponses to B application of SW41 and other sensitive genotypes at field sites of the first international Boron Probe Nursery (1990/91) confirmed that B deficiency can be a major cause of grain set failure in wheat in warm areas.     

Variation in responses to boron in rice

Background and aims

Boron (B) deficiency depresses grain set and grain yield of wheat and maize while having little effect on their vegetative growth. This paper describes effects of B deficiency in rice and how these vary with planting season and variety.

Methods

Three rice varieties (KDML105, CNT1, SPR1) were grown in sand culture without (B0) and with 10 μM (B10) B added to the nutrient solution, in the cool season of 2007/08 and 2008/09 and the hot season of 2011 in Chiang Mai, Thailand (18°47′N, 98°59′E). Boron responses were measured in growth and yield parameters, pollen viability and B concentration of the flag leaf and anthers at anthesis.

Results

Grain weight was strongly depressed by B deficiency ranging from 28 % in SPR1 to 79 % in CNT1, and the yield was much lower in the cool season than in the hot season plantings. The variation in grain weight was closely associated with grain set and number of spikelets but not with shoot dry weight or tillering. Grain set was closely related to pollen viability, and both were increased with increasing anther B concentration at >20 mg B kg^?1. In addition to its adverse effect on grain set, B deficiency also depressed grain filling and weight of individual grains in rice.

Conclusions

Boron deficiency depressed rice grain yield through adverse effects on reproductive growth, panicle and spikelet formation and grain filling, in addition to grain set as in wheat and maize.     

Xylem-solute technique to measure N2 fixation by Phaseolus vulgaris L.: Calibration and sources of error

Utilising the ¹⁵N dilution technique the relationship between the proportion of N derived from N₂ fixation and relative abundance of ureides in xylem sap was evaluated for Phaseolus vulgaris L. cv. Mokcham during vegetative and reproductive development. In order to establish calibration curves for time integrated estimates of N₂ fixation, plants were raised in sand culture during the dry season in northern Thailand and continuously supplied with a N-free nutrient solution or the same solution amended with 0, 3, 6 or 9 mol m^–3 nitrate. Large changes in plant dependence on N₂ fixation were concomitantly reflected by corresponding alterations in N solutes in xylem sap. Regression analyses of the data suggested high correlations between relative ureide content and N₂ fixation, but different slopes and line intercepts indicated the requirement for the use of calibration curves established for different phases of the development of the plant. Largest age related differences were noted between vegetative and reproductive development. Judging from 95% confidence limits, utilisation of appropriate calibrations can reduce errors of the technique to close to ±5%.A second experiment, involving similarly cultivated plants exposed to different sources of mineral N, indicated an effect of ammonium on xylem sap composition. This implies that calibrations, in which N₂ fixation is regulated only by applications of various concentrations of nitrate, may lead to errors in situations where a major proportion of the plant available soil nitrogen fraction is present in the form of ammonium.