Planting density and training in grafted indeterminate tomato plants grown under plastic cover

ABSTRACT Grafting in tomato is a regular production practice aimed to control vascular diseases. Even though grafted plants are more expensive, when a vigorous rootstock is used the plants can be trained using multiple leading shoots, reducing the number of plants per hectare. Seeking to reduce direct labor cost and the cost of the plants, this experiment tested 29,000, 26,000, 23,000 and 20,000 leading shoots/ha, training the plants with either 3 or 4 leading shoots each. Plants were grown in a polyethylene-covered greenhouse, transplanting at the end of January; the harvest was done from May until August, quantifying yield, fruit size and leaf area, analyzing the data with quadratic regression. Yield increased from 81 to 103 t/ha when comparing the lowest and the highest density of shoots/ha, but the difference between the training systems was only 4 t/ha. When the two extremes of the density were compared (29,000 vs 20,000 shoots/ha), leaf area increase by 2%, the equatorial fruit diameter increased from 7.4 to 7.8 cm, and the weight increased from 178 to 199 g/fruit. The training system showed difference of 0.1 cm in fruit diameter, while the leaf area and fruit weight were not affected. While the lowest density of shoots per hectare had a 30% reduction in direct labor cost, the largest net profit margin was observed when using 3 shoots/plant and 29,000 shoots/ha.

摘要 番茄嫁接是防控维管束病害（vascular diseases）的常规生产措施。尽管嫁接苗成本偏高，但若使用健壮砧木（vigorous rootstock），则可通过培育多个主枝（leading shoots）来降低每公顷的种植株数。为降低直接人工成本与种苗成本，本试验设置了29000、26000、23000及20000条主枝/公顷的密度梯度，每株分别保留3或4条主枝进行整枝。试验于聚乙烯覆盖温室（polyethylene-covered greenhouse）中开展，于1月底完成定植，采收期为5月至8月，期间测定了产量、果实大小与叶面积（leaf area），并采用二次回归（quadratic regression）对试验数据进行分析。结果显示，主枝密度从最低（20000条主枝/公顷）升至最高（29000条主枝/公顷）时，产量从81吨/公顷提升至103吨/公顷，但不同整枝方式间的产量差异仅为4吨/公顷。对比密度两极值（29000与20000条主枝/公顷），叶面积提升2%，果实横径（equatorial fruit diameter）从7.4 cm增至7.8 cm，单果重从178 g升至199 g。不同整枝方式仅在果实横径上存在0.1 cm的差异，对叶面积与单果重无显著影响。尽管每公顷主枝密度最低的处理可降低30%的直接人工成本，但以每株保留3条主枝、29000条主枝/公顷的组合，可获得最高净利润率（net profit margin）。