Effect of floricane number on primocane growth, yield components, and cold hardiness in 'Marion' trailing blackberry

Abstract

In spring of 1993 and 1994, mature 'Marion' (Rubus sp.) plants were pruned to 0, 4, 8, and 12 floricanes. An additional treatment of 0 floricanes with early (30 cm) primocane pruning was included. Primocane growth was measured from emergence in April until growth cessation at the end of October. Yield component analysis was completed after harvest during the first season and in the following season. Dry weight partitioning was determined in summer and winter. During the winter, cold hardiness of primocanes was determined by controlled freezing. In 1993, plants without floricanes produced more primocanes with a greater total length and showed a trend toward a greater number and length of primocane branches at the end of the season. In 1993, internode length was significantly reduced in plants with 0 or 4 floricanes compared to plants with 8 or 12 canes. In 1994, there were no significant differences in primocane growth among treatments. Primocane growth in all treatments occurred in flushes with plants without floricanes having a significantly higher absolute growth rate (AGR) on 5 dates compared to plants with floricanes in 1993. In 1994, there was no treatment effect on AGR over the season; however, plants without floricanes still had a greater primocane AGR than plants with floricanes on six dates before fruit harvest. During both years, there were approximately 5-7 peaks in AGR throughout the season. When comparing primocane growth at three phenological stages in 1993, plants with no floricanes had a significantly higher AGR during fruit production and from harvest to growth cessation than plants with floricanes. In 1994, plants with no floricanes had the highest rate of growth before bloom and a trend towards higher AGR during fruit production. After fruit production, there were no differences in AGR between the treatments in 1994. Plants with floricanes produced a second flush of primocanes while plants with no floricanes produced only one flush. Primocane length (averaged for 4, 8, and 12 floricane plants) of the first flush was significantly different from the second flush at all dates during the season except for the final end of season measurement. In 1993, primocane topping at 30 cm tended to decrease primocane number and total length. In 1994, there were no significant effects of topping except for increased branch length. Plants without floricanes produced primocanes that were significantly more cold hardy (lower LT₅₀) in 1994 and 1995 than plants with floricanes. All treatments had greater hardiness in 1995 than in 1994. In both 1993 and 1994, plants with four floricanes had significantly higher percent budbreak than plants with 12 floricanes. In 1993, plants with four floricanes also had significantly fewer nodes per cane, a shorter average cane length, reduced lateral length. and a lower number of branch canes compared to plants with 8 or 12 floricanes. In 1994, there were no variables affected by floricane number per plant other than percent budbreak. In 1993, there was no significant difference in yield between plants with 8 and 12 floricanes while plants with 4 floricanes had a lower yield. In 1994, yield per cane was significantly higher in plants with 4 floricanes compared to plants with 8 or 12 floricanes; yield per plant was not affected by floricane number. There were no significant treatment effects on berry weight in either year. In summer of 1993, there was a trend for a decrease in primocane dry weight and a significant decrease in branch dry weight with an increase in floricane number. Total plant, fruit, floricane and lateral dry weight increased linearly with increasing floricane number. Results were similar for floricane components in the summer of 1994, however, there were no treatment effects on primocane or branch dry weight. There was also a positive linear relationship between crown dry weight and floricane number in 1994. By the winter of 1994 and 1995, there were no treatment effects on primocane or crown dry weight. Plants without floricanes produced a significantly greater number of canes per plant than plants with floricanes in 1993 but not in 1994. Plants without floricanes produced primocanes that had a significantly lower percent budbreak the following year (1994) than plants with floricanes. There was a similar trend in 1995. Plants without floricanes had a higher number of nodes per branch and a greater average branch cane length than plants with 8 or 12 floricanes. Number of nodes per cane tended to decrease with increased floricane number per plant in 1994 and 1995. There was no significant treatment effect on fruit per lateral, berry weight or yield per plant in either 1994 or 1995. However, in 1994, plants without floricanes had the lowest yield per cane but the highest yield per meter of cane compared to plants with floricanes. Topping primocanes at 30 cm in 1993 had no significant effect on yield components the following season. The only variable significantly affected by pruning in 1994 was a reduction in fruit per lateral with primocane pruning. 'Marion' primocanes had a typical sigmoid growth curve similar to the growth pattern seen in red raspberry and other plants. Our findings of the emergence of two flushes of primocanes without primocane suppression and absolute growth rate occurring in peaks of growth throughout the season have not been previously reported in Rubus. Primocanes on plants with floricanes may have the ability to "catch up" to those on plants without floricanes after harvest as there were no differences in primocane dry weight by winter. In this study, we did not see an increase in yield in plants grown without floricanes the previous season as is generally found in 'Marion'. This may have been a result of winter training rather than primocanes being trained in the summer as they grew, a practice that improves light exposure to the canes. Yield compensation occurred through an increase in percent budbreak in plants with 4 floricanes compared to those with 8 or 12 canes.