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

- Differences in balsam fir NAR genotypes may be explained by ability to rehydrate.
- Water content decreases from 57% to 28% in 3 weeks when water is withheld.
- High NAR genotypes could recover after up to 7 days dehydration.
- Low NAR genotypes could not recover beyond 2 days of dehydration.

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 21 d before being provided water and evaluated for water content, xylem pressure potential, stomatal conductance, and needle abscission. Fresh branches were 57% water content at −0.5 MPa and rapidly declined over 21 d without water to approximately 28% water content at −7.0 MPa. The ability to rehydrate was different between low and high NAR genotypes; low NAR genotypes could only successfully rehydrate within 2 d of dehydration (51% water content, −2.8 MPa) while high NAR genotypes were able to rehydrate within 7 d of dehydration (36% water content, −4.9 MPa). There was no significant difference in postharvest abscission of contrasting NAR genotypes when dehydrated for up to 2 d, but high NAR genotypes had significantly lower abscission when water was withheld for 5 or 7 d. When dehydrated for 14 or 21 d, 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.