Different flowering response to various fruit loads in apple cultivars correlates with degree of transcript reaccumulation of a TFL1-encoding gene.
In many perennial fruit trees, flowering in the year following a year with heavy fruit load can be quite limited. This biennial cycle of fruiting, termed alternate bearing, was described 170 years ago in apple (Malus domestica). Apple inflorescences are mainly found on short branches (spurs). Bourse shoots (BS) develop from the leaf axils of the spur. BS apices may terminate ~100 days after flowering, with formation of next year's inflorescences. We sought to determine how developing fruit on the spur prevents the adjacent BS apex from forming an inflorescence. The presence of adjacent fruit correlated with reaccumulation of transcript encoding a potential flowering inhibitor, MdTFL1-2, in BS apices prior to inflorescence initiation. BS apices without adjacent fruit that did not flower due to late fruitlet removal, neighbouring fruit on the tree, or leaf removal, also reaccumulated the MdTFL1-2 transcript. Fruit load and gibberellin (GA) application had similar effects on the expression of MdTFL1-2 and genes involved in GA biosynthesis and metabolism. Some apple cultivars are less prone to alternate bearing. We show that the response of a BS apex to different numbers of adjacent fruit differs among cultivars in both MdTFL1-2 accumulation and return flowering. These results provide a working model for the further study of alternate bearing, and help clarify the need for cultivar-specific approaches to reach stable fruit production.
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Amnon
A
Haberman
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Michal
M
Ackerman
Migal-Galilee Technological Center, Kiryat Shmona, Israel.
Omer
O
Crane
INRA, UMR AGAP, AFEF team (Architecture and functioning of fruit species), Montpellier, France.
Jean-Jacques
JJ
Kelner
INRA, UMR AGAP, AFEF team (Architecture and functioning of fruit species), Montpellier, France.
Evelyne
E
Costes
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Alon
A
Samach
D000069599:Crop Production; D035264:Flowers / Q000235:genetics / Q000254:growth & development*; D005638:Fruit / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D017343:Genes, Plant / Q000502:physiology*; D005875:Gibberellins / Q000378:metabolism; D027845:Malus / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development / Q000502:physiology
D005875:Gibberellins; D010940:Plant Proteins
Malus domestica; TERMINAL FLOWER 1; alternate bearing; flowering; fruit load; genetic variation