Differences in dehydration rate and ability to rehydrate in contrasting needle abscission resistant balsam fir genotypes

Abstract

Postharvest needle abscission is a major challenge in balsam fir with respect to postharvest Christmas tree quality. It is hypothesized that differences in dehydration rate or ability to rehydrate may contribute to observed differences in needle abscission resistance (NAR). Branches were collected from low and high NAR genotypes and dehydrated for 0, 1, 2, 5, 7, 14, or 21d before being provided water and evaluated for water content, xylem pressure potential, stomatal conductance, and needle abscission. Fresh branches were 57% water content at −0.5MPa and rapidly declined over 21d without water to approximately 28% water content at −7.0MPa. The ability to rehydrate was different between low and high NAR genotypes; low NAR genotypes could only successfully rehydrate within 2d of dehydration (51% water content, −2.8MPa) while high NAR genotypes were able to rehydrate within 7d of dehydration (36% water content, −4.9MPa). There was no significant difference in postharvest abscission of contrasting NAR genotypes when dehydrated for up to 2d, but high NAR genotypes had significantly lower abscission when water was withheld for 5 or 7d. When dehydrated for 14 or 21d, no branches were able to recover and abscission occurred rapidly. It was concluded that low NAR genotypes were unable to recover from a similar water content as high NAR genotypes, which contributes to genotypic differences in postharvest abscission rates.