培養液中Ca濃度が根域制限栽培したトマト果実の 水溶性Ca濃度と尻腐れ果発生に及ぼす影響

The rate of absorbed Ca to N was less than half of Enshi or Hoagland solution in tomato (Solanum lycopersicum Mill.) grown with restricted root zone volume in previous experiments. Tomato plants were grown in plastic pots containing 250 or 500ml of peat based medium with modified Enshi solutions containing 1, 2 or 4mM of Ca. The solutions were prepared by replacing a part of Ca(NO3)2・4H2O to NH4NO3. Although Ca concentration was higher than 2mM in drainage collected from plants supplied 1mM Ca solution, absorbed amount of Ca was very small and severe symptom of Ca deficiency was observed. Incidence of blossom-end rot (BER) increased with decrease in Ca concentration of the solution and yield decreased to 50% and 36% of 4mM control, in 2mM and 1mM plots, respectively. Among fractionated Ca in stem of lateral shoot, decrease in water-soluble fraction was remarkable compared to 1N NaCl- or 0.6N HCl-soluble fractions. Tomato plants were then grown with modified solutions containing 1~4mM of Ca and fractionated Ca was determined for distal half of fruits. With decrease in solution Ca, fruit Ca decreased in all fractions, and days to BER incidence after flowering also decreased. Significant relationship was found only between the water-soluble Ca concentration in fruit tissue and rate of BER incidence. Thus water-soluble Ca in tomato fruit may closely relate to BER incidence, and an efficient tool to estimate the potential risk of BER may possibly be developed by determining the Ca fraction in the stem of lateral shoots.

根域制限下におけるトマトの養分吸収を調査した結果，培養液中Caの多くは排液とともに排出され，Ｎに対するCaの吸収比率は園試処方やHoagland処方中の比率の50%以下であった．そこで，園試処方培養液中のCa(NO3)2･4H2Oの一部をNH4NO3に置換してCa濃度１，２，４ﾋの培養液を作成し，日射比例給液制御下で ‘ハウス桃太郎’の根城制限栽培（培地容量250，500 ㎖）を行った．培養液のCa濃度が１ﾋであっても排液中のCa濃度が２ﾋよりも高く推移したが，Ca吸収量は極めて少なく，著しいCa欠乏症状が現れた．低Ca濃度区では尻腐れ果が多発し，１ﾋ区では第３果房より上段の果実は全て尻腐れ果となり，第９果房までの収量は２ﾋ区，１ﾋ区でそれぞれ４ﾋ区の50%，36%に低下した．腋芽茎中のCa濃度の低下は0.6N-NaCl可溶性画分や0.6N-HCl可溶性画分と比較して水溶性画分の低下が著しかった．そこで，Ca濃度が１～４ﾋの培養液を用いて点滴栽培を行い，果実中のCa濃度を分画して定量した．果実頂部のCa濃度はいずれの画分においても培養液中Ca濃度が低いほど低く，開花から尻腐れ症状が発生するまでの日数も短くなった．尻腐れ果発生率と果頂部の水溶性Ca濃度との間にのみ有意な負の相関が認められた．以上のことから，果実の水溶性Ca濃度がトマトの尻腐れ果発生リスクの大小に大きくかかわっており，植物体の水溶性Ca濃度測定は尻腐れ果発生防止のためのCa栄養診断に応用できる可能性が高いと考えられる．

原著論文 (Original paper)