Source: PURDUE UNIVERSITY submitted to
UNDERSTANDING FLOWERING AND FRUIT GROWTH OF APPLE
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0175221
Grant No.
(N/A)
Project No.
IND011824
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2004
Project End Date
Sep 30, 2009
Grant Year
(N/A)
Project Director
Hirst, P. M.
Recipient Organization
PURDUE UNIVERSITY
(N/A)
WEST LAFAYETTE,IN 47907
Performing Department
HORTICULTURE
Non Technical Summary
It is difficult to produce high yields of apple fruit that are of the most desirable size. This project examines the genetic limitations on fruit size.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2011110104050%
2041110102050%
Goals / Objectives
The goal of this research is to gain further understanding of flowering and fruit growth in apple, and examine the relationship between flower development and fruit development. Specific objectives are: 1. Measure the time of flower induction of 5 apple cultivars using gene expression as an indicator. 2. Anatomically follow the time-course of floral bud differentiation of 5 cultivars from the time of initiation until full bloom. 3. Measure both the rate and duration of cell division in 5 apple cultivars to determine the contributions of receptacle size at flowering, rate of cell division, cell production rate, duration of cell division and cell expansion to final fruit size. 4. Identify and clone genes associated with cell division in apple and relate the expression of these genes to the observed patterns of cell division.
Project Methods
Objective 1: Analysis of the time of floral induction based on the expression of LFY genes. The AFL1 gene will be amplified and cloned from Gala using PCR primers based on the available sequence of the gene. The degree of expression of this gene should help us pinpoint the time at which the floral signal is received within the bud. We will also study two large-fruited mutants of Gala that our previous research has shown endo-reduplicate only in floral tissue. We hypothesize that the change to polyploidy in these buds will occur soon after expression of AFL1 is detected. The time of floral induction is important, since earlier induction allows more time for differentiation of the bud prior to bloom the following year (objective 2). Objective 2: Relationships between time of floral induction, flower bud differentiation and fruit size potential. We will anatomically follow floral differentiation and development of the receptacle tissue starting at the time of floral induction (as determined in Objective 1), through the dormant period and up to the time of bloom. Buds will be sampled periodically from 5 cultivars differing in their fruit size potential. The degree of bud development will be rated under a dissecting microscope using a visual rating scale developed in our previous work. At bloom, the number of cells in the receptacle tissue will be estimated . Objective 3: Dynamics of fruit growth. The genetic control of apple fruit development will be determined in five apple cultivars as listed above. Fruit growth will be monitored in each of these cultivars from just prior to full bloom until harvest by measuring the diameter of selected flowers/fruits. On each measurement date, additional fruit will be harvested for cytological analysis, to determine cell number and cell size. Relationships between the rate and duration of cell division, and the cell production rate with fruit size across the cultivars will be determined. Objective 4: Isolation and expression of key cell cycle control genes in apple. Using a differential gene expression approach we will determine which genes are expressed preferentially during the cell division period in apple. A cDNA-AFLP will be used. These sequences will be compared to existing databases to assign a putative function to these genes. Probes to screen the cDNA library for cyclin and CDK genes will be made by RT- PCR using degenerate oligonucleotide primers based on their highly conserved homology across plant species (Joubes et al., 2000). We predict that these genes will show a cell division phase-specific expression and a reduced expression upon the end of cell division and initiation of cell expansion. This pattern of developmentally regulated expression would enable us to use these genes as markers to follow the state of cell division in apple fruit during further studies. This study will enable us to address the question of whether the abundance of these key cell cycle gene transcripts is limiting fruit size in apple.

Progress 10/01/04 to 09/30/09

Outputs
OUTPUTS: Experiments have been conducted to study flowering and fruit growth in apple. Key experiments conducted are: 1. Developmental comparison of vegetative, flowering (non-fruiting) and fruiting spurs of Gala (annual bearing) and Fuji (biennial bearing). 2. Comparison of growth of Gala and Red Delicious fruit in terms of cellular dynamics under differing source-sink conditions. Results have ben reported at the following conferences: American Society for Horticultural Science (2004, 2009), Washington State Horticultural Association annual meeting (2009), XIV International Symposium on Apple and Temperate Zone Fruit Trees, Cuauhtemoc, Mexico (2008), South West Michigan Horticultural Days (2008), Minnesota Apple Growers Association annual meeting (2007), Illinois Specialty Crop and Agritourism Conference (2007), Department of Horticulture seminar, University of Cairo, Egypt (2006), Rosaceae Genomic Conference, Napier, New Zealand (2006), International Fruit Tree Association annual meeting (2006), Ohio Fruit and Vegetable Growers Conference (2006) and Wisconsin Fruit and Vegetable Conference (2004). Multiple presentations have been given to indiana growers at the Indiana Horticultural Congress and at smaller county extension meetings. One PhD student has graduated during this project (2005). PARTICIPANTS: Anish Malladi, graduate student worked on the project conducted experiments to examine the genetic control of fruit size in apple (PhD completed December 2005). Partner organization: Washington Tree Fruit Research Commission - made financial contributions and staff assisted with research experiments. TARGET AUDIENCES: Target audiences: 1. Fruit growers in Indiana, the United States and abroad. 2. Scientists interested in the physiology and genetics of flowering and fruit size control. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Findings have been communicated to growers and scientists via presentations in Indiana, Washington, Pennsylvania, Michigan, Minnesota, Illinois, Ohio, Wisconsin, Arizona, and Texas. in addition, research results were presented in Egypt, New Zealand, Hungary and Mexico. Changes in knowledge have occurred as a result of this research. Key findings are: 1. Floral and fruiting status had no effect on bud development, in terms of the proportion of buds forming flowers, or the timing of flower differentiation. Annual (Gala) and biennial (Fuji) cultivars behaved similarly in this respect. This contrasts with conventional wisdom and has the potential to alter the ways growers manage their apple orchards. 2. Size accumulation of Gala and Red Delicious fruit were similar and the only reason Red Delicious were larger at harvest was due to their delayed maturity period. This was true over 3 growing seasons. 3. Changes in source-sink ratios (using thinning to reduce crop load levels) affected Gala and Red Delicious similarly. Crop load induced differences in fruit size were mainly the result of changes in cell number rather than cell size. 4. Increased early season temperatures resulted in larger fruit size primarily by increasing cell size. 5. A large fruited mutant of Gala exhibited an altered form of the cell cycle, and was not representative of the dynamics of fruit size increase in other apple cultivars.

Publications

  • Malladi, M. and Hirst, P.M. 2010. Increase in fruit size of a spontaneous mutant of Gala apple (Malus x domestica Borkh) is facilitated by altered cell production and enhanced cell size. J. Exp. Bot (submitted).
  • Hirst, P.M. and Malladi, A. 2008. A new understanding of fruit size. The Compact Fruit Tree (Special issue 2008).


Progress 10/01/07 to 09/30/08

Outputs
OUTPUTS: A second year of data was collected from Gala and Fuji spurs on which flowering had been manipulated. Flower development was measured on spurs that were vegetative, flowered but defruited, or bearing fruit. Diurnal differences in fruit growth of two cultivars (Silken and Pink Lady) was measured precisely using dendrometers. Results have been communicated to apple growers in Michigan at the Southwest Michigan Horticultural Days meeting, and also at a number of county fruit meetings in Indiana. PARTICIPANTS: Washington Tree Fruit Research Commission, Purdue University Fruit Extension Team TARGET AUDIENCES: Scientists and fruit growers nation wide. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Flowering status of spurs of Gala and Fuji did not affect the quantity of flowers that developed for the following season's crop. Furthermore, flowering status of spurs did not affect the degree of floral bud differentiation. It appears that localized effects may be secondary to overall tree crop loads. There appeared to be little difference in the diurnal pattern of fruit growth of Silken and Pink Lady apples.

Publications

  • No publications reported this period


Progress 10/01/06 to 09/30/07

Outputs
OUTPUTS: Flower bud development of Gala (a regular flowering cultivar) and Fuji (a biennial flowering cultivar) buds was studied. The time and degree of flower formation was studied along with the level of bud differentiation. Fruit growth of Red Delicious and Gala fruit was studied from flowering until harvest in response to 2 crop load levels. The size of the fruit was compared with patterns of change in cell size and cell number. Results were presented to members of the Washington Tree Fruit Research Commission at their research review, the Minnesota Apple Growers at their annual meeting and the Indiana fruit industry at a number of county extension meetings. PARTICIPANTS: Wahington Tree Fruit Research Commission TARGET AUDIENCES: Target audiences are scientists and extension workers in the fruit industry nation wide, and fruit growers across the country. Efforts designed to cause a change in actions are presentations to the Washington Tree Fruit Research Commission, the Minnesota Apple Growers Association annual meeting, and Indiana fruitgrowers by means of numerous presentations at county extension meetings.

Impacts
Flowers developed in buds of Fuji earlier in the season than buds of Gala. However by the end of the season, a high proportion of all buds formed well-developed flowers. The time of flower formation did not appear to be related to the degree of flower bud initiation. The presence of fruit on a spur did not affect flower bud formation in Gala, but with Fuji fruit delayed the time and complexity of flower bud formation. This may have implications for both fruit set and fruit growth the following year. Fruit diameter of Gala and Red Delicious was similar throughout the season, and the larger fruit size at harvest of Red delicious was due to a later harvest date. This result needs to be corroborated with multiple years data. Reduced crop load resulted in larger fruit size, mainly via an increase in cell number. The difference in fruit weight of Red delicious vs Gala was due to the product of small differences in cell size and cell number.

Publications

  • No publications reported this period


Progress 10/01/05 to 09/30/06

Outputs
Flower initiation was studied in 10 new apple cultivars and the pattern of bud differentiation over the course of the season described. Cultivars in which flower initials were observed in more than 90 percent of buds were CQR10T17, Zestar and NJ90, whereas those with fewer than 50 percent of buds forming flowers were September Wonder, Silken, Ambrosia, Delblush and Sundance. These data were closely correlated with the flower ratings taken the following spring in the field. For all cultivars, flower bud differentiation occurred mostly during July and early August, however the probability of floral committment was earliest in CQR10T17 and most rapid and concentrated in NJ90. The timing of floral committment is important since it may be related to the overall degree of flower initiation and therefore the propensity of a cultivar for biennial bearing, a significant problem for apple industries around the world.

Impacts
These results provide further information on the how the degree of flowering and perhaps also on how the quality of flowers is regulated in different apple cultivars. The degree of flowering relates to biennial bearing and the quality of flowers may influence fruit size. Biennial bearing and poor fruit size are both practical problems faced by apple growers.

Publications

  • No publications reported this period


Progress 10/01/04 to 09/30/05

Outputs
We have cloned four genes from apple that appear to be involved in the cell cycle. Of these, Md;CycB2, Md;CycD3, and Md;CDKB1 were expressed during times of high activity of the cell cycle while another, Md;CDKA, exhibited little phase specificity of expression. Therefore we have identified 3 genes that may be regulators of fruit size.

Impacts
Of the many potential regulators of the cell cycle, we have cloned and identified 3 that may regulate the cell cycle and thereby affect fruit size in apple.

Publications

  • Hoover, E., N. De Silva, S. McArtney and P. Hirst. 2004. Bud development and floral morphogenesis in four apple cultivars. J. Hortic. Sci and Biotech. 79: 981-984.


Progress 10/01/03 to 09/29/04

Outputs
We have cloned 4 cell-cycle genes that are expressed in apple fruit cortical tissue. Two of these, CDK B1 and Cyc B2, appear to be expressed only during the cell divsion stage of fruit development. These genes may play a role in regulating the intensity and duraton of cell division, and thereby influence fruit size.

Impacts
This work will enable us to better understand the process of flower development from the time of floral initiation, through to flowering, and fruit growth. A better understanding of this process is essential to developing practical protocols of advantage to commercial producers.

Publications

  • No publications reported this period


Progress 10/01/02 to 09/30/03

Outputs
We have completed the work on bloom delay, with treatments resulting in up to 9 days of delay in the time of bloom. Due to the expense of treatments however, it is unlikely these are commercially feasible. We have characterized large-fruited apple mutants, and found that they have increased leaf photosynthetic capacity, and increased sink strength, seemingly resulting from higher ploidy levels. These mutants however are fruit specific polyploids (beginning early during floweral differentiation), and undergo about 4 rounds of endoreduplication. Cloning of cell cycle genes is progressing and we aim to determine the levels of expression of these genes in times of high fruit cell division and compare expression levels in mutants versus wild types.

Impacts
This work will enable us to better understand the process of flower development from the time of floral initiation, through to flowering, and fruit growth. A better understanding of this process is essential to developing practical protocols of advantage to commercial producers.

Publications

  • Hirst, P.M. 2002. Frost damage does not predispose apple fruitlets to the effects of chemical thinners. Hort Technology 12(1): 1-3.
  • Hirst, P.M. 2003. Flower bud formation, pollination and fruit set. In: Concise Encyclopedia of Temperate Zone Tree Fruits. Eds: T.A. Baugher and S. Singha. Hawthorn Press, New York.


Progress 10/01/01 to 09/30/02

Outputs
We have been studying flower formation and development in the Gala cultivar along with two mutants which have substantially greater fruit size. Differences in fruit size were apparent as early at the flowering stage of development. Furthermore the mutants both exhibited polyploidy in flowering and fruiting tissue, but not in vegetative tissue. No polyploidy was found in any tissues of the wild type material.

Impacts
This work is contributing to the further understanding of the flowering process of apple, both in terms of flower initiation and flower development. Eventually we hope to be able to manipulate the genes responsible for flower development resulting in larger fruit size.

Publications

  • No publications reported this period


Progress 10/01/00 to 09/30/01

Outputs
Field studies investigating bloom delay treatments on peaches have been completed. Data have been analyzed and 3 papers are ready to be submitted for publication. Some of the treatments were effective in delaying bloom for up to 9 days, resulting in significant risk reduction in terms of frost damage to flowers. These treatments however were very expensive and would not prove cost-effective for peach growers to use at the present time. There was also some variability in how effective these treatments were from one year to another, and a model has been developed to explain this variation.

Impacts
A model has been proposed to describe mechanisms of bloom delay and explains the year to year variation that was observed with some treatments. Although not cost effective, we have shown that bloom in peaches can be delayed for up to 9 days using these treatments. These data are ready to be submitted for publication and may stimulate further research in this area.

Publications

  • Hirst, P.M. 2001. Flower bud formation, pollination and fruit set. In: Concise Encyclopedia of Temperate Zone Tree Fruits. Ed: T.A. Baugher and S. Singha. Hawthorn Press. (in press).


Progress 10/01/99 to 09/30/00

Outputs
Initial studies evaluating bloom delay treatments on peaches have been extended with another series of experiments carried out over the past year. AVG applications effectively delayed bloom by 2-5 days. The most effective treatment was two applications of 2000 ppm AVG, which delayed bloom by almost 5 days. Repeat applications of AVG were more effective than the single dosage treatments. The 1000 ppm, repeat application delayed bloom by 4 days. A single application of 5000 ppm AVG resulted in severe phytotoxicity. AVG, apparently, delayed bloom by delaying bud development following the completion of rest. Dormant oil sprays were ineffective in achieving bloom delay

Impacts
Our studies indicate that AVG is effective in delaying bloom in peaches by 5 days. This has the potential to substantially increase peach yields in years with a late spring freeze. However at current market prices, these treatments are not cost effective for a grower to apply.

Publications

  • Tu, Y. and P.M. Hirst. 2000. Endogenous gibberellins in developing apple seeds in relation to biennial bearing. HortScience 35(3):487. (abstract)
  • Malladi, A. and P.M. Hirst. 2000. Effect of AVG and dormant oils on bloom delay in 'Redhaven' peach. HortScience 35(3):495. (abstract)


Progress 10/01/98 to 09/30/99

Outputs
Dissection of potential floral buds from a genotype/environment/thinning study is continuing and is nearly complete. Once all the buds have been dissected, data can be analyzed and publication of results will proceed. Seeds of 2 genotypes differing in their propensity for biennial bearing has been completed for a second year. Extraction of gibberellins from these tissues is underway and the quantification of 5 different GA's is proceeding. The efficacy of a range of tretments in delaying bloom of peach has been evaluated. Applications of oils prior to budbreak was ineffective, however AVG applications did result in bloom delay. Studies are continuing to determine whether this acts by extending the chilling requirement or merely delaying growth in the spring.

Impacts
One more year's data are required to complete several of these studies and then definitive conclusions from them may be drawn.

Publications

  • No publications reported this period


Progress 10/01/97 to 09/30/98

Outputs
Meristem samples of 3 apple genotypes growing in 3 environments have been collected at various times throughout the growing season. Initial observations suggest a large genotype influence on flower induction in close proximity to seeds, however more detailed analysis of the data is still in progress. In another study, seeds from 2 genotypes were collected at intervals throughout the growing season and immediately frozen. Qualitative and qualitative analyses of gibberellin levels is currently underway.

Impacts
(N/A)

Publications

  • No publications reported this period