Osmoregulative capacity in birdseed millets (Setaria italica L. and Panicum miliaceum L.) in response to water stress
Summary of PhD thesis
Birdseed millets (Setaria italica L. or Panicum miliaceum L.) are intolerant of long dry periods and incapable of recovering after being drought stressed. This is partly because it has a relatively shallow root system The improvement of birdseed millet yield stability under water stress conditions i.e. its drought resistance is needed.
This study aimed to examine the variation in osmoregulative capacity among birdseed millets (S. italica and P. miliaceum) accessions and in the F3 generation following a crosses between two parents of S. italica differing in expression of this character. Components contributing to solute accumulation and associations between osmoregulative capacity and grain yield, morphological or physiological characters were also determined.
To examine variation in osmoregulative capacity, 11 accessions of S. italica and 14 accessions of P. miliaceum were used, to represent a wide range of variability in morphological background. Experiments were conducted at The Tamworth Centre for Crop Improvement and The University of Queensland Gatton.
Plants were grown in pots in a glasshouse and after they had reached the booting stage, they were transferred to a controlled environment cabinet. Osmoregulative capacity was measured in flag leaves of headed plants undergoing a water stress, which had been imposed by withholding water.
The group of accessions of S. italica showed an overall level of osmoregulative capacity which was greater than that observed for the group of P. miliaceum accessions. Four accessions of S. italica (108042, 108463, 108541 and 108564) and one accession of P. miliaceum (108104) demonstrated high osmoregulative capacity. Differences of 1.05 MPa or more between observed and estimated osmotic potential were found at relative water contents of 80% among these accessions. Accessions with high osmoregulative capacity could maintain turgor pressure, as indicated by lower values of leaf water potential at full turgor.
The extent of osmoregulative capacity found was associated with osmotic potential at full turgor and the rate of decline in osmotic potential as leaf water potential declined. Variation in this character was not associated with any variability in morphological backgrounds, such as plant height, inflorescence shape, stem thickness, numbers of tillers or the amount of dry matter produced.
In a glasshouse experiment, accessions of S. italica (108042) and P. miliaceum (108104) with high osmoregulative capacity showed a slower decline in leaf area development and photosynthetic rate than accessions with low osmoregulative capacity (108040 and 109009 P. miliaceum, respectively), as water stress developed. Solute accumulation in the leaf tissues of the accessions with high osmoregulative capacity was not due to reductions in leaf area.
Total sugars was the major component contributing to solute accumulation in leaf tissues observed as result of a water stress treatment in an accession with high osmoregulative capacity. Proline and calcium also increased as water stress developed, but their contributions to solute accumulation were relatively small.
In a field experiment, a S. italica accession with a high osmoregulative capacity (108541) demonstrated a higher photosynthetic rate and higher transpiration rate and a lower stomatal resistance than an accession with a low osmoregulative capacity (108046), under stress conditions. A significant association between photosynthetic rate and stomatal resistance indicated that inhibition of photosynthetic rate had occurred as water stress developed, mainly resulting from stomatal factors. Water use efficiency was significantly higher for the accession with the high osmoregulative capacity than for the accession with the low osmoregulative capacity, after seven weeks of withholding water. This indicated that a higher transpiration rate was not costly for the accession with the high osmoregulative capacity, because it was apparently compensated for by a higher acquisition of carbon dioxide.
Differential response to water stress in Setaria italica associated with higher osmoregulative capacity in the accession on the right
In both glasshouse and field experiments, accessions with high osmoregulative capacity produced a higher grain yield than accessions with low osmoregulative capacity. This high grain yield resulted from maintenance of photosynthetic rate, the production of more grain numbers and a low percentage of empty florets.
In the field experiment using F3 families derived from crossing between low and high osmoregulative capacity accessions osmoregulative capacity appeared to be simply inherited. Segregation into 23 low and 17 high osmoregulative capacity F3 families was compatible with a single gene model, if a recessive gene controlled this character. Among the F3 families, osmoregulative capacity was not associated with plant height, flag leaf length, flag leaf width, panicle exersion, inflorescence length, inflorescence width or weight of 100 seeds, but was highly associated with grain yield and harvest index. Mean grain yield and harvest indices for the high osmoregulative capacity group were 1.58 and 1.57 times greater than those of the low osmoregulative capacity group, respectively.
In the F3 families, the percentage of empty florets for the high osmoregulative capacity group were higher than for the low osmoregulative group. The extent of osmoregulative capacity was significantly associated with the percentage of empty florets when measured 20% or 40% of the distance from the base of the panicle. The association between grain yield and the percentage of empty florets was also significant. The coefficient correlation between grain yield and the percentage of empty florets was higher at 40% (r=-0.83**) than 20% (r=-0.69**) of the length from the panicle base. The percentage of empty florets for spikes at 40% of the length from the panicle base, therefore, may be useful as indicator of sensitivity to water stress conditions.
Osmoregulative capacity is thus an important character for use as a selection criterion for drought resistance. Breeding for higher yield under water limited conditions using this character in birdseed millet is possible since variation in this character is available and is associated with grain yield.
Fletcher, R.J., Mitchell, S.P. and Karyudi. (1996) Improvement program for the millet/panicum industry. Proceedings, 8th Australian Agronomy Conference, Toowoomba, February, 1996, 651.
Karyudi and Fletcher, R.J. Variation in osmoregulative capacity in birdseed millet under conditions of water stress and its lack of association with variability in morphological backgrounds. (Accepted by Field Crops Res.).
Karyudi and Fletcher, R.J. Variation in osmoregulative capacity under conditions of water stress for F3 lines of birdseed millet and its relationship with plant morphology and yield. (Submitted to Field Crops Res.).
Karyudi and Fletcher, R.J. (1999) Leaf area, photosynthesis and yield under conditions of water stress for birdseed millet accessions differing in osmoregulative capacity. In Proceedings, 11th Australian Plant Breeders' Conference, Adelaide, April, 1999. 2pp.
Karyudi and Fletcher, R.J. (1999) Osmoregulative capacity in Setaria italica L. (Foxtail millet) and Panicum miliaceum L. (Proso millet) in response to water stress after heading. In Proceedings, 11th Australian Plant Breeders' Conference, Adelaide, April, 1999. 2pp.
Karyudi, and Fletcher, R.J. (1996) Change in photosynthetic rate, stomatal resistance and transpiration in Panicum miliaceum and Setaria italica demonstrating different osmoregulative capacity under water stress. Proceedings, Fourth Annual Research Conference, The University of Queensland Gatton, October, 1996, 67.
Contact: Dr Rob Fletcher, School of Agriculture and Horticulture, The University of Queensland Gatton, 4343; Telephone: 07 5460 1311 or 07 5460 1301; Facsimile: 07 5460 1112; International facsimile: 61 7 5460 1112; Email:email@example.com
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Latest update 30 October 2000 by:RF