Plant Growth Regulators Improve Sweet Cherry Fruit Quality without Reducing Endocarp Growth

Sweet cherry fruit growth is divided into three phases that are described classically as (1) cell division, (2) endocarp lignification, and (3) cell expansion. Negligible fruit size increase during stage II suggests that the endocarp is the dominant sink in the fruit at this stage. It is not known whether endocarp lignification competes with pericarp development for carbohydrate resources. We investigated this by attempting to reduce lignin accumulation and endocarp sink strength. Several plant growth regulators, include N-(2-Chloro-4-pyridyl)-N'-phenylurea (CPPU), GA1, GA3, GA4/7, and fluridone (inhibitor of ABA biosynthesis) were applied in lanolin paste to ‘Bing' fruit pedicels at the onset of stage II of fruit development. Fluridone (0.1%) alone or plus GA1 (500 ml l-1) increased fruit size significantly (+ 15%) though these increases were not associated with a decrease in pit weight. Further, GA1 alone did not increase fruit size, seed or endocarp weight, which suggests that ABA metabolism during pit hardening might be involved in mesocarp growth. Although GA3 and GA4/7 alone did not affect seed growth, they increased endocarp dry weight by 11%. CPPU did not increase fruit weight or pit weight, but did reduce seed growth and induced ca. 85% aborted seeds. Overall, final fruit weight was not correlated well with weight of pit, endocarp, or seed. These results demonstrate potential to manipulate sweet cherry fruit growth by manipulating hormonal balance.