Parthenocarpic fruit development in Capsicum annuum

 

Key words: Parthenocarpy, Capsicum, fruit set, hormones, cell division, cell expansion,

auxin, gibberellin, temperature, carpel-like structures, genotype

 

Parthenocarpy (fruit set without fertilization) is a much desired trait in sweet pepper

(Capsicum annuum) production as it minimizes yield irregularity, enhances total

yieldandmakes theproduction possible under suboptimal environmental conditions. Beside

this, parthenocarpyimproves the commercial value of the fruitsince parthenocarpic fruits

are convenient for consumption, much wanted for minimal-processed food, and possess

long shelf-life.Parthenocarpy has been widely studied for tomato and Arabidopsis but not for

C. annuum.Physiological and morphological characterization of parthenocarpy in C.

annuum is the main focus of this thesis with emphasis on finding evidence thattomato and

Arabidopsis can be used as model plants to study fruit development in C. annuum.The

series of physiological and morphological changes (i.e. pollen tube growth, vascular

connection between ovule and carpel, cell division and cell expansion in carpel) that occurs

in a post-fertilized ovary ofC. annuumwas similar to that reported in tomato and

Arabidopsis. Similar to these two species, C. annuum showed a hierarchy between auxin

and gibberellinwhere auxin acts upstream of gibberellin in fruit set, most likely by inducing

gibberellin biosynthesis.These findings indicate that fruit set mechanisms in C. annuum are

similar to that reported in tomato and Arabidopsis.Parthenocarpy was evident in most of the

studied genotypes of C. annuum(n=24) suggesting that somedegree of intrinsic

parthenocarpy is already present in C. annuum. External application of auxin and

gibberellin on the stigma of emasculated flowers enhanced parthenocarpic fruit

production.GA3 did not significantly contribute to the final fruit size. GA3 seems to play an

important role in preventing flower and fruit abscission while auxin seems to be important

for both fruit set and fruit development.

Almost all seedless fruits obtained either by only emasculation or emasculation followed by

hormone application showed stronger growth of carpel like structures (CLS) compared to

seeded fruits. Structural analogy of CLS with bel1 mutant of Arabidopsis suggests that CLS

are transformed from abnormal ovules.Capsicum genotypes with high parthenocarpic

potential showed a stronger CLS development suggesting a relation between female

sterility and parthenocarpy. The parthenocarpic potential appeared to be controlled by a

single recessive gene. The CLS phenotype and parthenocarpy could not be linked to a

single locus, suggesting that absence of fertilization induces parthenocarpic fruit

development and allows CLS growth, which substitutes developing seeds in promoting fruit

development.This thesis provides insight in the physiology and morphology and genetic

basis of parthenocarpy in C. annuum.