Patterns and Strength of Pollen Tube Arrest in Self–incompatible Citrus Accessions (Rutaceae)

Abstract

Pollen tube growth was examined to demonstrate the degree of self-incompatibility reaction in the pistils of 121 Citrus accessions including 77 pummelo accessions. One hundred of the 121 accessions were determined to be self-incompatible with the aid of an epifluorescent microscope. Based on the difference of self pollen tube growth between the self-incompatible and self-compatible accessions, the degree of selfincompatibility reaction in four portions of the pistils was roughly divided into three categories, i.e., high (H), moderate (M) and low (L). The degrees of the reaction in the stigmas, upper styles, middle styles and basal styles of these accessions were high-high-high-high (H-H-H-H), moderate-high-high-high (M-H-H-H), moderate-moderate-high-high (M-M-H-H), low-high-high-high (L-H-H-H), low-moderate-highhigh (L-M-H-H) or low-low-high-high (L-L-H-H) in order from the stigma to lower style, and were designated as H, MH, MMH, LH, LMH and LLH types respectively. All of 77 pummelo accessions examined were self-incompatible and all of the seven types of self-incompatibility reaction were observed in the accessions of which about 80% showed either H or MH type of reaction. The degree of self-incompatibility reaction was more variable in the pummelo accessions originating in Southeast Asia than those in Japan. In three mandarin relatives and four yuzu relatives, the H and MH types of self-incompatibility reaction were exclusively found. These results suggested that the degree of self-incompatibility reaction in each part of style was different in different Citrus accessions and showed geographical diversity. The reason for this is discussed.

Genotyping of Citrus Accessions with S9 and/or S10 Alleles for Self-incompatibility and Their Allelic Distribution

“…All Citrus accessions and homozygous S 1 seedlings (S 9 S 9 and S 10 S 10 ) were trees more than ten years old, grown in the Experimental Farm of Kyushu University, Sasaguri, Fukuoka. Self-incompatibility in these accessions had been determined through the observation of pollen tube arrest in their style base eight days after self-pollination (Ngo et al, 2019).…”

“…S 4 S ? z Self-incompatibility (**) and semi-self-incompatibility (*) in most accessions are based on the report of Ngo et al (2019), and the others depend on the following reports: present study, Kim et al (2010Kim et al ( , 2011Kim et al ( , 2020, Soost and Roose (1969), Yamamoto et al (2006), Vardi et al (2000) and Zhou et al (2018). y Fresh S 9 pollen was collected from HBS3, HBS4, HBS19 and HBS25 with the S 9 S 9 genotype, while S 10 pollen was collected from HBS2, HBS11 and HBS20 with the S 10 S 10 genotype.…”

“…These results suggested that self-incompatibility in a given Citrus accession could be determined only by observation of the pollen tubes in the basal style (Ngo et al, 2019).…”

“…], mandarin (Citrus spp. ), and their hybrids (Soost, 1987;Yamamoto et al, 2006;Kim et al, 2011;Ngo et al, 2019). SI is an important trait for breeding and seedless fruit production in Citrus cultivars with a high degree of parthenocarpy (Iwamasa and Oba, 1980;Vardi et al, 2000).…”

“…For Citrus, however, there is very limited information about the self-incompatibility S gene sequence (Honsho et al, 2019;Liang et al, 2020), S allele variation, S allele frequencies, and the S genotypes of cultivars (Kim et al, 2020). Ngo et al (2019) studied the patterns and strength of self-incompatibility in 121 Citrus accessions, including 77 self-incompatible pummelos. They found that the degree of SI in the stigmas, upper styles, middle styles, and basal styles of the self-incompatible pistils differed and could be divided into three categories: high, moderate, and low.…”