ACC (1-aminocyclopropane-1-carboxylic acid) deaminase producing endophytic bacteria improve hydroponically grown lettuce in the greenhouse during summer season

Abstract

In the summer, cool season crops like lettuce are typically not grown in a greenhouse because evaporative coolers cannot sufficiently lower the temperature to their optimal range (12–18 °C). The objective of this study was to increase yields of two butterhead lettuce cultivars (‘Buttercrunch’ and ‘Rex’) under summer heat stress utilizing bacterial endophytes with high 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. ACC is a precursor of ethylene. ACC deaminase reduces stress in plants by cleaving ACC into α-ketobutyrate and ammonia and lowering ethylene levels. Four bacterial endophytes (IALR387, IALR1385, IALR1794 and IALR1819) having high levels of ACC deaminase activity were selected from the Plant Endophyte Research Center's bacterial endophyte collection. The endophytes were identified as either Paraburkholderia sp. (IALR387 and IALR1385) or Burkholderia contaminans (IALR1794 and IALR1819). These 4 bacterial endophytes were tested in ‘Buttercrunch’ and ‘Rex’ during summer 2022 in two greenhouse experiments. The inoculation of lettuce with these bacterial endophytes enhanced lettuce growth in greenhouse hydroponic production except for IALR1385. In both cultivars, IALR1819 improved lettuce growth the most with shoot fresh and dry weights and the chlorophyll content.