Precocious genotypes and homozygous tendency generated by self-pollination in walnut

Area of Science:

• Plant Genetics
• Horticulture
• Breeding

Background:

• Observations of early-bearing walnut (Juglans regia L.) genotypes prompted investigation into the genetic basis of precocity.
• Iron walnut (Juglans sigillata Dode), an ecotype of J. regia, was studied for its self-fertility and progeny characteristics.

Purpose of the Study:

• To investigate the origin and genetic control of precocious traits in walnut.
• To analyze the self-fertility, progeny performance, and genetic variation of Juglans sigillata.

Main Methods:

• Self-pollination of Juglans sigillata cv. 'Dapao' (DP) was conducted, and fruit set and seed germination rates were recorded.
• Nine self-pollinated progeny (SP1-SP9) were selected, and their flowering times were compared to the typical period.
• Twelve simple sequence repeat (SSR) markers were used to analyze the genetic variation and homozygosity in selected progeny and the parent genotype.

Main Results:

• Self-pollinated seeds of 'Dapao' showed moderate germination rates (45.2%) and evidence of inbreeding depression.
• Four progeny (SP1-SP4) exhibited precocious flowering, initiating flowers at 2 years old, significantly earlier than the typical 7-10 years.
• Analysis revealed a tendency toward high homozygosity in the genomes of self-pollinated progeny, consistent with other precocious walnut genotypes.

Conclusions:

• Self-pollination in walnut can generate precocious phenotypes with highly homozygous genomes.
• This process may facilitate the development of unique homozygous parents for future walnut breeding initiatives.
• Precocious walnut trees require careful management to mitigate potential early-life production depression.