施钾时期对葡萄转色和品质及钾吸收基因表达的影响

  【目的】  钾肥可促进葡萄果实的提前着色，本研究比较了不同时间施用钾肥对葡萄转色和品质的影响，并从分子水平初步验证了钾肥施用时期对葡萄转色的效果。  【方法】  以江苏盱眙、浙江天台和浙江金华3个地区的5年生‘夏黑’葡萄为试材，分别在果实膨大后4 (T1)、8 (T2)、12 (T3)、16 (T4)天的上午10:00，沟施120 g/株 K₂SO₄水溶肥，以不施钾肥为对照。在每次处理前观察果实颜色，处理后每隔4天统计果实转色率，并采集30粒果实用于测定果实纵横径、果粒重、硬度、可溶性固形物(SS)、可滴定酸(TA)等生理指标。于施肥处理前1 h (上午9:00)，采集葡萄第8～9节位成熟叶片4～5片，用于检测VvKUP1、VvKUP2荧光定量相对表达量。  【结果】  4个施肥时期沟施120 g/株钾肥后，3个地区施肥处理均促进了葡萄果实提前转色。与对照相比，在江苏盱眙和浙江金华均以T3处理促进着色效果最好，果实分别提前4和8天左右着色，转色率分别达到95.0%和80.6%；在浙江天台以T2处理促进果实着色效果最好，提前4天左右着色，转色率达到83.4%。沟施钾肥可以促进果粒重和纵横径的增加，在江苏盱眙和浙江金华均以T3处理最好，在浙江天台以T1处理最好。在江苏盱眙，4个沟施钾肥处理均提高了果实可溶性固形物含量，T2、T3、T4处理降低了果实硬度；在浙江金华地区，4个施钾处理均降低了果实可滴定酸含量和果实硬度，提高了可溶性固形物含量；在浙江天台，沟施钾肥降低了果实可滴定酸含量和果实硬度，T1、T2、T3处理提高了可溶性固形物含量。通过对不同时期‘夏黑’葡萄叶片中钾吸收基因的表达分析，发现当钾吸收基因VvKUP1表达趋势由下降转为上升，且VvKUP2表达趋势由上升转为下降时，与最适施肥时期相符合。  【结论】  沟施钾肥可以促进‘夏黑’果实提早着色和果实品质的提高。果实膨大后12天施钾肥在江苏盱眙和浙江金华地区促进‘夏黑’葡萄转色的效果较好，果实膨大后8天施钾肥促进浙江天台地区‘夏黑’葡萄的转色效果较好。葡萄膨大后叶片中两个钾吸收关键基因(VvKUP1和VvKUP2)表达量的变化证明了该时期施钾的必要性。

Effects of potassium fertilizer application time on the coloration and quality of grape fruit and the expression of potassium-absorbing genes

  【Objectives】  A sufficient potassium (K) supply benefits the grape coloring and taste quality. Here, we studied the effect of potassium fertilizer application times on berry coloration and grape quality and evaluated the necessity of applying K at specific periods using gene expression profiles.   【Methods】  Field experiments were conducted in Xuyi of Jiangsu Province and Tiantai and Jinhua of Zhejiang Province, using 5-year-old ‘Summer Black’ grape as test materials. The treatments were four K₂SO₄ application times, including 4 days (T1), 8 days (T2), 12 days (T3), and 16 days (T4) after fruit expansion, at an application rate of 120 g/plant K₂SO₄. No K fertilization was used as the control. Sample color was observed before each treatment, and the fruit coloring rate was counted every 4 days after the treatment, and 30 fruits were collected for the determination of fruit equatorial diamete and polar diameter, fruit weight, firmness, soluble solids (SS), and titratable acid (TA). One hour before K fertilization (9: 00 am), 4?5 pieces of mature leaves at nodes 8?9 were collected to determine the relative expression levels of VvKUP1 and VvKUP2.   【Results】  In Xuyi, Jinhua, and Tiantai, T3, T3, and T2 exhibited the best coloring effect of 95.0%, 80.6%, and 83.4%, respectively; T3, T3 and T1 had higher fruit weight, equatorial diamete and polar diameter, respectively. In Xuyi, all K treatments increased fruit SS content, and T2, T3, and T4 treatments reduced fruit firmness. In Jinhua, all treatments reduced the TA content and firmness but increased the SS content of the grape. In Tiantai, all treatments reduced the fruit TA content and firmness, and T1, T2, and T3 increased the SS content. Before and after K fertilization, there was a paradigm shift in the expression of the VvKUP1 gene from a decreasing to an increasing trend, and the expression of the VvKUP2 gene followed the opposite direction, consistent with the optimum fertilization period.   【Conclusions】  Potassium fertilizer can induce fruit coloring and improve fruit quality. Applying K₂SO₄ at 12 days after fruit expansion had a better influence on the grape ‘Summer Black’ in Xuyi and Jinhua, and application at 8 days after fruit expansion had a higher impact on the grape ‘Summer Black’ in Tiantai. The observed gene (VvKUP1 and VvKUP2) expression change verified the suitable K application time in the three tested cities.