Abstract

Media summary

Key Words

Water consumption, Phaseolus vulgaris, Snap bean, Temperature, Shoot extension

Introduction

Global warming includes many different effects such as high temperature, high CO₂ and high variability of rainfall. Snap bean (Phaseolus vulgaris L.) often undergoes high temperature stress during pre- and post anthesis period in the subtropical Okinawa islands of Japan. However, high temperature also causes high evaporation and transpiration, resulting in drought and water deficit in soil and plants. In cabbage, a comparison of heat tolerant and sensitive cultivars indicated that head formation at high temperature was associated with aspects of water relation (Kuo et al. 1988). Nakano et al (1998) observed that high temperature 15-25 days before anthesis was also detrimental. Therefore, there is increasing evidence that high temperature may not directly affect the reproductive parts, but may have indirect effects through decreasing the plant water status and changing other components of the tissue water relations. Water status may be associated with heat tolerance. However, there are only few reports (Tsukaguchi et al. 2003) on the effects of high temperature on the water status of snap bean. Therefore, a better understanding of the influence of high temperature on plant water relations is necessary to identify the plant process that confers temperature tolerance to snap beans. This study evaluated the effects of water and high temperature stresses on leaf water status in snap beans and the association of these phenomena in tolerant (Nakano et al. 1997) and sensitive cultivars.

Materials and Method

Two snap bean cultivars, ‘Haibushi’ (HB), heat tolerant cultivar and ‘Kentucky Wonder’ (KW), heat sensitive cultivar were used for the experiments at subtropical Ishigaki islands, Okinawa, Japan.

Summer production of snap bean.

The seeds were sown on May 13, 2003 in a shade house with 62% transmission of solar radiation. Planting space was 25cm (plant to plant) x 1.2m (row to row). Ten seedlings were allowed to grow in one plot. The numbers of flowers and pods that reached harvest size were counted every two or three days after the first flower appeared.

Water consumption and shoot extension of snap bean

The seedlings were grown in a soil (mixture of 80% clay soil +20% compost) mixed with 0.03% lime and applied 0.03% NPK in equal quantities under 24/20°C (12/12hr, day/night) or 27/23°C under natural light conditions. Relative humidity in the greenhouses was maintained at 70±10%. Ten cm diameter plastic pot containing 800g, and 17.5cm pots containing 4,000g dry soil were used for the experiment. Three or four seeds were sown per pot after the soil was saturated with water. The seedlings were thinned to one per pot in small pots and 2 per pot in large pots when the first trifoliate leaf appeared. The seedlings were transferred to greenhouses maintained at low (24/20°C), normal (27/23°C) and high (31/27°C) temperature one week after flower opened or at the true leaf stage. Water consumption of each pot was measured during the day (7:00 AM – 7:00 PM) and night (7:00 PM – 7:00 AM) by the gravimetric method for 5 days. The weight reduction of the pot containing only soil was used for data correction. Leaf weight was measured after all measurement had finished. Water consumption per solar radiation during the day time was obtained by conversion to the water consumption per equal leaf area (5,000 cm²). Five days of data for each treatment were plotted in the figure. Accumulated solar radiation was calculated by multiplication by 0.61 (screen factor through the glass) using the data recorded at the meteorological station of the Okinawa subtropical station of the Japan International Research Center for Agricultural Science, Japan located 160m from the experimental site The shoot extension was measured during the day (7:00 AM – 7:00 PM) and at night (7:00 PM – 7:00 AM) after the seedling was fully watered at 3:00 PM on Nov. 7

Results

Summer production of snap bean

Figure 1. No. of open flowers and pods harvested from different snap bean (Phaseolus vulgaris L.) cultivars. a: ‘Haibushi’ (heat tolerant), b: ‘Kentucky Wonder’ (heat sensitive). Each ten plants were cultivated in 3m² plot.

After the first flower open on June 12, HB increased the number of open flowers, reached a maximum on June 25, and gradually decreased thereafter (Figure 1). Pod harvesting started on June 23. Pod recorded maximal harvesting on June 30, and finished on July 14th. KW started to open flowers on June 25th, recorded maximal flower opening on June 30th, and finished on July 7th. There were no pods harvested from KW. Mean temperature during pod harvesting in HB was 31.8°C.

Water consumption and shoot extension of snap bean

HB showed temperature-independent water consumption, while KW showed temperature- dependent water consumption during the night time (Figure 2). HB did not show any changes in water consumption at low and high temperatures, maintaining high consumption compared to KW at a low temperature when the value per fresh leaf weight was compared. KW, on the contrary, showed changes in water consumption at the different temperatures, that is, low consumption at low temperatures and high consumption at high temperatures. Water consumption in KW at high temperature was the same as that in HB at low temperature.

Figure 2. Relation between fresh leaf weight and water consumption during the night. □ : ‘Haibushi’ at 24/20°C, ■ : ‘Haibushi’ at 31/27°C, ○ : ‘Kentucky Wonder’ at 24/20°C, ● : ‘Kentucky Wonder’ at 31/27°C, Regression line ( - : ‘Haibushi’ at 24/20°C, - : ‘Haibushi’ at 31/27°C, - : ‘Kentucky Wonder’ at 24/20°C, - : ‘Kentucky Wonder’ at 31/27°C ).

Water consumption per solar radiation during the day time tended to differ depending on the cultivars (Figure 3). Water consumption of HB showed higher values compared to KW at low temperature. Water consumption increased at a high temperature in both cultivars. However, the increase was greater in KW.

The shoot extension also tended to differ depending on the cultivar (Figure 4). KW showed temperature-dependent shoot growth, while HB showed temperature-independent shoot growth. The shoot in KW extended more at normal than low temperature, and reduced its extension at high temperature. The shoot extension in HB, on the contrary, did not change at different temperatures, maintaining same level of KW at low temperature.

Conclusion

‘Haibushi’, heat tolerant snap bean (Phaseolus vulgaris L.) cultivar, consumed an abundance of water independent of temperature, contributing to higher yield during the summer in subtropical Ishigaki islands, Japan. Shoot extensibility may be one of the key functions of maintaining water consumption at higher level.

Figure 3. Relation between accumulated solar radiation and water consumption during the day. □ : ‘Haibushi’ at 24/20°C, ■ : ‘Haibushi’ at 31/27°C, ○ : ‘Kentucky Wonder’ at 24/20°C, ● : ‘Kentucky Wonder’ at 31/27°C, Regression line ( - : ‘Haibushi’ at 24/20°C, - : ‘Haibushi’ at 31/27°C, - : ‘Kentucky Wonder’ at 24/20°C, - : ‘Kentucky Wonder’ at 31/27°C ).

Figure 4.Shoot extension of 2 snap bean cultivars under different temperatures. ■ : ‘Haibushi’ at 24/20°C, ■ : ‘Haibushi’ at 27/23°C, ■ : ‘Haibushi’ at 31/27°C, ● : ‘Kentucky Wonder’ at 24/20°C, ● : ‘Kentucky Wonder’ at 27/23°C, ●: ‘Kentucky Wonder’ at 31/27°C.

References

Kuo, C. G.., B. J. Shen, H. M., Chen, H. C. Chen and R. T. Opena 1988 Associations between heat tolerance, water consumption, and morphological characters in Chinese cabbage, Euphytica 39: 65-73

Nakano, H., M. Kobayashi and T. Terauchi 1998 Sensitive stages to heat stress in pod setting of common bean (Phaseolus vulgaris L.). Jpn. J. Trop. Agr. 42(2): 78-84

Nakano, H., T. Momonoki, T. Miyashige, H. Otsuka, T. Hanada, A. Sugimoto, H. Nakagawa, M. Matsuoka, T. Terauchi, M. Kobayashi, M. Oshiro, K. Yasuda, N. Vanichwattanarumruk, S. Chotechuen and D. Boonmalison 1997. “Haibushi”, a new variety of snap bean heat tolerant to heat stress. JIRCAS J. 5: 1-12

Tsukaguchi, T. Y, kawamitsu, H. takeda, K. Suzuki and Y. Egawa 2003 Water status of flower buds and leaves as affected by high temperature in heat-tolerant and heat-sensitive cultivars of snap bean (Phaseolus vulgaris L.). Plant Prod. Sci. 6: 24-27