Varietal Differences in CO_2 Assimilation Rate and Leaf Area Increasing Rate and Their Changes in Breeding Process of Sweet Potato Plants

This study was carried out to know varietal differences in net CO_2 assimilation rate and leaf area increasing rate and their changes in breeding process of main cu1tivars of sweet potato improved in Japan. The cultivars used in this study were 7 native cultivars, 14 cultivars bred before 1955 and 10 cultivars bred after 1955 (Table 1). They were grown in pot culture for measurement CO_2 assimilation and transpiration, and in field for survey of leaf area increasing rate, respectively. Rates of CO_2 assimilation and transpiration were simultaneously measured by a climatic-controlled assimilation chamber method in September, 1982. Leaf area increasing rate was calculated from multiplication of leaf emergence rate and mean area per leaf for 12 days surveyed in September, 1982. Results obtained were as follows, 1. There were large varietal differences in CO_2 assimilation rate. However, most of improved cultivars were higher in CO_2 assimilation rate as compared with native cultivars. 2. There also were varietal difference in transpiration rate. Transpiration rate of improved cultivars was higher than that of native cultivars. 3. There was a high positive correlation between CO_2 assimilation rate and transpiration rate. Most of improved cultivars were higher in both rates of CO_2 assimilation and transpiration as compared with native cultivars. 4. There were large differences in dark respiration rate. Cultivars bred after 1955 were larger than that of cu1tivars bred before 1955. 5. Leaf conductance had high positive correlations with CO_2 assimilation rate and transpiration rate, respectively. Leaf conductance values in improved cu1tivars were higher than that of native cultivars. 6. CO_2 assimilation rate had significant positive multiple-correlation with leaf conductance and mesophyⅡ conductance. However, CO_2 assimilation rate correlated more closely with mesophyⅡ conductance than leaf conductance MesophyⅡ conductance was larger in improved cultivars as compared with native cultivars. 7. Leaf emergence rate (A), mean area per leaf (B) and leaf area increasing rate (A×B) in cultivars bred after 1955 were larger as compared with ones bred before 1955. Furthermore, specific leaf area (SLA) in improved cultivars was larger than that of native cultivars. 8. It was made clear from mentioned above that most of cultivars bred after 1955 had high abilities of CO_2 assimilation and leaf area increasing. At the same tame, it suggests that crossing and selection in breeding process of sweet potato in Japan were performed for increase of abilities in CO_2 assimilation and leaf area production with balance of them.本研究はわが国におけるサツマイモの品種改良に関わってきた主要な31品種を供試し,光合成速度と葉面積生産速度の品種間差と交雑育種過程における両能力の変遷について明らかにしたものである.その結果以下の諸点が明確になった.1.光合成速度は品種によって変異は大きかったが,在来品種に比べて育成品種では,一般的に高い傾向が認められた.2.蒸散速度も品種による変異はみられたが,在来品種に比べ育成品種が大きかった.3.光合成速度と蒸散速度との間には高い正の相関関係がみられ,育成品種では光合成速度,蒸散速度がともに高い傾向にあった.4.暗呼吸速度は品種による変異が大きく,一般的傾向は認められなかったが,昭和30年以降の育成品種で大きかった.5.光合成速度及び蒸散速度と拡散伝導度は共に密接な相関々係を有し,拡散伝導度は在来品種に比べ,育成品種で大きかった.6.光合成速度は拡散伝導度と共に葉肉伝導度とも高い正の相関関係にあった.重相関解析から葉肉伝導度は拡散伝導度よりも光合成速度と密接な関係にあることが明らかになった.7.葉肉伝導度は在来品種に比べ育成品種で大きくなる傾向が認められた.8.昭和30年以降の育成品種はそれ以前の育成品種に比べて出葉速度と平均一葉面積が大きく,両者の積である葉面積生産速度は大きかった.また比葉面積は小さくなる傾向が認められた.9.以上から昭和30年以降に育成された品種の多くは,高い光合成速度と葉面積生産速度を兼ね備えていることが明らかになった.10. サツマイモの品種育成過程では光合成速度と葉面積生産速度がバランスよく向上するように交雑組合せと選抜が行われてきていることが推定された.本研究を行うに当たり供試材料を分譲下さった元九州農業試験場作物第2部作物第2研究室長坂本敏氏に対し心から感謝の意を表します