A hypersensitive response-like reaction is involved in hybrid weakness in F₁ plants of the cross <i>Capsicum annuum</i> × <i>Capsicum chinense</i>

Abstract

Hybrid weakness in Capsicum is characterized by the termination of leaf differentiation after the development of several leaves. F 1 plants in some crosses between Capsicum annuum and Capsicum chinense show weakness; this phenomenon has not been investigated in detail since first reported. In the present study, we characterized morphologically and physiologically hybrid weakness in Capsicum . F 1 plants did not show weaker growth than their parents 20 days after germination (DAG), but at 40 DAG, the hybrid weakness phenotype was evidenced by almost complete arrest of new leaf formation, delayed increase in plant height, and reduced upper internode length. The shoot apical meristem (SAM) of F 1 plants exhibited delayed development and an abnormal structure characterized by a flat shape and the presence of fuzzy cell layers on the surface. These abnormal SAMs of F 1 plants may lead to dwarfism. Dead cells and accumulation of H 2 O 2 were visually detected in leaves of F 1 plants, and cell death was considered to be programmed, as it was accompanied by internucleosomal fragmentation of DNA. The expression of immunity marker genes PR1 and PR2 was upregulated in leaves of F 1 plants. These results suggest that a hypersensitive response-like reaction is involved in Capsicum hybrid weakness.

Parental Genome Imbalance Causes Hybrid Seed Lethality as Well as Ovary Abscission in Interspecific and Interploidy Crosses in Nicotiana

“…Conspecific pollen precedence and gametic incompatibility are examples of post-mating prezygotic isolating barriers ( Rieseberg and Willis, 2007 ). In turn, postzygotic isolation barriers include enlarged ovary (immature fruit) abscission ( Gupta et al, 1996 ; He et al, 2019 ), seed abortion or hybrid seed lethality ( Coughlan et al, 2020 ; Dziasek et al, 2021 ), hybrid weakness ( Shiragaki et al, 2019 , 2020 ), hybrid lethality ( Kawaguchi et al, 2021 ; Si et al, 2021 ; Tezuka et al, 2021 ; Mino et al, 2022 ), and hybrid sterility ( Li et al, 2020 ) in seedlings of the F 1 generation, as well as hybrid breakdown recognized in generations after the F 1 ( Matsubara et al, 2007 ; Zhang et al, 2021 ). These isolating barriers may be observed independently or combined, even in a single cross-combination.…”

Capsicum annuum with causal allele of hybrid weakness is prevalent in Asia

“…The seedlings were cultivated in a constant-temperature room (25˚C, 12 h light and 12 h dark, 85 μmol m -2 s -1 ). At 60 days after germination, the genotypes of each accession were determined as the aaBB genotype if all F 1 hybrid plants did not obtain the first flower due to growth arrest, a characteristic of Capsicum hybrid weakness [20], and the aabb genotype if all F 1 hybrid plants received the first flower and continued to grow.…”

“…Therefore, it is possible that the causal gene contributes to disease resistance [36,37]. Similarly, Capsicum hybrid weakness has been shown to cause an autoimmune response [20], and Ballele of Capsicum hybrid weakness may have been used in the breeding process.…”

“…Hybrid weakness, formerly called as "hybrid dwarfism,", is observed in some reciprocal crosses of C. annuum × C. chinense or C. annuum × C. frutescens [11,12]. F 1 hybrids having hybrid weakness show cessation of growth approximately 40 days after germination and a hypersensitive response-like reaction, including H 2 O 2 accumulation, programmed cell death, and upregulation of defense-related genes in leaves [20]. Capsicum hybrid weakness is caused by two complementary dominant genes, and it has been reported that C. annuum can exhibit the aaBB genotype, whereas C. chinense and C. frutescens exhibit only the AAbb genotype.…”

Two Nicotiana occidentalis accessions enable gene identification for Type II hybrid lethality by the cross to N. sylvestris

“…Seed abortion, hybrid lethality and hybrid sterility in the F 1 generation as well as hybrid breakdown in subsequent generations are examples of postzygotic barriers. Hybrid lethality has been reported in many systems including a great number of crop species 4 – 12 .…”