Crop Genetics - Control Hybridization — Self-incompatibility, Male-sterility, and Sex-inheritance

Why are fertility-regulating mechanisms important in crop breeding?

They control self- vs. cross-pollination and can be obstacles or tools for producing hybrids and desired crosses.

What is self-incompatibility (SI)?

The inability of a plant to set seed after self-pollination despite viable pollen; cross-pollination succeeds.

What is the natural purpose of self-incompatibillity?

Promotes outcrossing, maintains heterozygosity, and reduces inbreeding depression.

How does self-incompatibility work genetically?

Compatibility is determined by genetic interactions between pollen and pistil SI alleles.

What do SI genes regulate?

Whether pollen germinates, pollen tubes grow, or fertilization occurs.

What is gametophytic self-incompatibility (GSI)?

Compatibility depends on the allele carried by the pollen grain itself.

Where is pollen inhibited in GSI?

In the style, when pollen and pistil SI alleles match.

What is sporophytic self-incompatibility (SSI)?

Compatibility depends on the SI genotype of the pollen-producing plant.

Where is pollen inhibited in SSI?

At the stigma surface, often due to dominant incompatible alleles.

What is bud pollination?

Pollinating flowers before SI mechanisms are fully active.

What is pseudo-compatibility?

Environmental conditions temporarily suppress SI expression.

How can breeders genetically overcome SI?

By introducing self-fertility (Sf) alleles.

What is male sterility?

Failure to produce functional pollen or anthers while female fertility remains normal.

Why is male sterility useful in breeding?

It prevents self-pollination and eliminates the need for manual emasculation.

What is genetic male sterility (GMS)?

Male sterility controlled by nuclear genes, usually recessive (ms).

Why is stable expression important in GMS?

Complete sterility across environments ensures reliable hybrid seed production.

What is cytoplasmic male sterility (CMS)?

Male sterility controlled by mitochondrial genes inherited maternally.

What are A, B, and R lines in CMS systems?

A line: Male sterile

B line: Maintains sterility

R line: Restores fertility in hybrids

What is engineered male sterility?

Sterility introduced through genetic engineering, often linked to selectable traits.

What are chemical gameotides?

Chemicals that suppress pollen formation, though sterility may be incomplete.

What does sex inheritance refer to in plants?

Genetic determination of male and female flowers, especially in dioecious species.

What is dioecy?

Male and female flowers occur on separate plants.

How is sex determined in asparagus?

By sex chromosomes (XX = female, XY = male).

What is a “supermale” in asparagus breeding?

A YY male used to produce all-male offspring.

How is sex inheritance controlled in cucumber?

Through multiple autosomal genes influenced by environmental factors.

What flower types can occur in cucumber?

Male, female, hermaphrodite, or monoecious plants.

Why is understanding SI important for breeders?

It helps control pollination and manage crossing strategies.

How does male sterility improve hybrid seed production?

It enforces cross-pollination without manual labor.

Why is sex inheritance useful in hybrid breeding?

It allows control of seed parents and simplifies hybrid seed schemes.

What is the overall benefit of these mechanisms in controlled hybridization?

They enable efficient, reliable hybrid production while maintaining desired traits.