Beneficial Role of 1-Methylcyclopropene for Cut Lupinus havardii Racemes Exposed to Ethephon

Abstract

The raceme of Lupinus havardii Wats. (Big Bend bluebonnet) is a new greenhouse specialty cut flower, but postharvest life is limited by ethylene sensitivity. The authors studied the effects of 160 nL·L−1 1-methylcyclopropene (1-MCP) with 0 to 6 days exposure to a 50-μm vase solution of ethephon [(2-chloroethyl) phosphonic acid, CEPA] on raceme postharvest quality indices and mature flower cell membrane permeability. With no CEPA, 1-MCP delayed postharvest losses in fresh weight and mature flower retention, and extended vase life longevity (VLL) by 1 to 4 days relative to a non-1-MCP control. With 2 days or more of CEPA, 1-MCP deferred raceme fresh weight loss and the abscission of both mature and newly opened flowers from 3 days to 5 days. There was a relatively strong protective effect of 1-MCP on raceme fresh weight, flower retention, and newly opening flowers in the presence of CEPA compared with the absence of CEPA. The greatest raceme VLL (7.2 days) was obtained for 1-MCP-treated racemes that did not receive CEPA in the vase. Although VLL was reduced by CEPA, VLL was consistently greater (by ≈2 days) after 1-MCP treatment relative to no 1-MCP treatment and irrespective of CEPA's duration. As expected, electrolyte leakage increased with individual flower development and between 1 day and 6 days in the vase. Unexpectedly, however, the 5-day postharvest increase in leakage was intensified by 1-MCP treatment if the racemes were exposed to 1 hour of CEPA in the vase solution. Electrical conductivity measurements suggested that, in the latter treatment (+1-MCP, +CEPA), increased levels of diffusible electrolytes that had yet to be exported to the expanding apical meristem (delayed raceme development) contributed to the higher leakage. Results also demonstrate good potential for quality maintenance of L. havardii racemes by using 1-MCP, and that in addition to flower retention, raceme fresh weight and flower opening should be considered in developing VLL criteria for this new specialty crop.