Drought stress and high light effcts on leaf photosynthesis.

Abberton, M. T., Macduff, J. H., Marshall, A. H., Humphreys, M. W. (2008). The genetic improvement of forage grasses and legumes to enhance adaptation of grasslands to climate change. United National Climate Change Conference, Nusa Dua, Bali, Indonesia, 3-14 December 2007, 39 pp. RONO: DB 05225

The genetic improvement of forage grasses and legumes to enhance adaptation of grasslands to climate change

Photosynthetic Physiological Response ofMedicago sativatoOdontothrips lotiDamage

Five experiments were conducted to investigate the effect of drought and high temperature stress on the growth and development of bambara groundnut (Vigna subterranea (L.) Verdc). Three glasshouse experiments were conducted at the University of Nottingham, Sutton Bonington Campus, UK, and two field experiments were conducted at the Botswana College of Agriculture, Gaborone, Botswana. In the glasshouse experiments, two landraces were grown, S19-3 (from hot, dry environment/ Namibia) and Uniswa Red (from cool, wet environment/ Swaziland) under two different temperatures, 33±5 oC and 23±5 oC. In the first experiment (2006), soil moisture was non-limiting. In the second experiment (2007) drought was imposed at pod filling stage (77 DAS). In the third experiment (2008), the same two landraces were grown under the same temperatures, but the drought was imposed at flowering (30 DAS). In the first field experiment, two landraces were grown under three sowing dates and two water regimes; rain fed and drought. The two landraces were Dip C (from hot, dry environment/ Botswana) and Uniswa Red. Drought was imposed approximately at pod filling (63 DAS). In the second field experiment, the same landraces were grown under the same sowing dates and water regimes with drought imposed at 30 DAS.

Canopy development and growth were affected by temperature and water stress. In the glasshouse experiments, Uniswa Red always gave the highest leaf number at the high temperature and S19-3 had the lowest at the low temperature. Leaf number decreased with drought, it reached over 100 in the full irrigation treatment, and less than 100 in late season drought treatment and a maximum of 60 in the early season drought treatment. Crops grown under high temperature always had higher leaf area index and total dry matter. The highest yield (306 gm-2) was produced by S19-3 at 33°C in 2007 and the lowest (31.1 g m-2) by Uniswa Red at 33°C in 2008. Comparison of regressions showed no significant difference in water use efficiency (WUE) between treatments in 2007. However, there were significant differences in 2008 when S19-3 (1.80 g kg-1) had a greater WUE than Uniswa-Red (1.09 g kg-1) at the high temperature, but both landraces had similar WUE at the low temperature (S19-3 2.28 g kg-1, Uniswa Red 2.23 g kg-1). This indicates that, despite being from a hot, dry environment, S19-3 performs well at the low temperature, and this is supported by data from 2007 when S19-3 maintained the highest soil moisture content and the lowest evapotranspiration at the low temperature. For the field experiments, where the temperature decreased with delay in sowing, there was a reduction in development, growth and yield. The effect of sowing date on leaf number was significant in both field experiments. In the first field experiment, the four treatments mean of leaf number of leaves declined from 62 per plant in the first sowing date (D1) to 52 leaves per plant in the third sowing date (D3) and 46 leaves per plant in the fifth sowing date (D5) and it was 64, 52, and 37 for D1, D3, and D5 respectively in the second field experiment. WUE decreased with delay in sowing from average of 1.9 g kg-1 in D1 to average of 0.45 g kg-1 in D5.

The landraces varied in their response to temperature and drought stress with respect to growth, development and resource capture and conversion. The landraces used different mechanisms to resist drought and temperature stress, that include high leaf water content, reduction in leaf area to reduce transpiration surface and avoidance through faster growth rate.

The effect of temperature and drought stress on Bambara groundnut (Vigna subterranea (L.) Verdc) landraces

Axonopus compressus (Sw.) Beauv. is a perennial herb widely used as a garden lawn grass. In this study, we used Roche 454 pyrosequencing, combined with the magnetic bead enrichment method FIASCO, to isolate simple sequence repeat markers from the A. compressus genome. A total of 1942 microsatellite loci were identified, with 53,193 raw sequencing reads. One hundred micro-satellite loci were selected to test the primer amplification efficiency in 24 individuals; 14 primer pairs yielded polymorphic amplification products. The number of observed alleles ranged from two to six, with an average of 3.5. Shannon's Information index values ranged from 0.169 to 0.650, with an average of 0.393. Nei's genetic diversity values ranged from 0.108 to 0.457, with an average of 0.271. This first set of microsatellite markers developed for Axonopus will assist in the development of molecular marker-assisted breeding and the assessment of genetic diversity in A. compressus.

/pdf/isolation-and-characterization-of-microsatellite-markers-for-ofrbl3tjus.pdf

Isolation and characterization of microsatellite markers for Axonopus compressus (Sw.) Beauv. (Poaceae) using 454 sequencing technology.

Three promising tropical forage legumes, Cratylia argentea, Flemingia macrophylla and Desmodium velutinum were evaluated in a tropical monsoon environment in Hainan Province, China. D. velutinum had higher net photosynthetic rate (P N ) and water use efficiency (WUE) than the other two species, and photosynthetic performance was consistent with their stomatal conductance (g s ). Responses in g s to increasing photosynthetically active radiation (PAR) showed two phases. Light was the main trigger for opening stomata at low light intensity (0–400 µmol quanta/m2/s), as was a reduction in intercellular CO 2 (C i ). Indirect actions contributed more to stomatal behaviour than the direct effect of light at intermediate to intense light intensity (400–2000 µmol quanta/m2/s), with water status being the major factor that controlled stomatal behaviour. D. velutinum was more affected by vapour pressure deficit (VPD) feedback regulation in intense light, and less by C i at low light intensity than were the other two species.

Radiation use and stomatal behaviour of three tropical forage legumes

A study on the photosynthetic physiological characters of the vegetative tillers and reproductive tillers of Axonopus compressus reveal that the net photosynthetic rate (Pn) and the water use efficiency (WUE) of the former are higher than those of the latter, while the respiration rate and the light compensation point (LCP)of the reproductive tillers are higher than those of vegetative tillers. Moreover, the reproductive tillers' basal leaves are weak in photosynthetic capacity and their respiratory intensity is intermediate-stronger than that of the vegetative tillers but weaker than the respiratory intensity of the flag leaves of the reproductive tillers. As the apparent quantum yield (AQY) of modules of the two tillers of Axonopus compressus are higher than those of plants in general, the lawn grass thrives in the dim light and adapts itself to a shady habitat. The vapor pressure deficit (VID) of leaves is mended through the stomatal conductance(Gs) to modulate the loss of water by the feedback of transpiration(Tr) .in the intense light, the stomatal conductance of modules of the two tillers descend gradually, but their transpiration rate and vapor pressure deficit continue to increase linearly. The fact shows that Axonopus compressus lacks a water-retaining machanism and is more adaptable to a water-saturated habitat.

A study on photosynthetic physiological characters of vegetative and reproductive tillers of {\sl Axonopus compressus}

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Radiation use and stomatal behaviour of three tropical forage legumes

A study on photosynthetic physiological characters of vegetative and reproductive tillers of {\sl Axonopus compressus}