A recent article posted on Phys.org notes that hybrid agricultural and horticultural crops can play an important role in supporting global food security. They produce higher yields and are often more resistant than non-hybrid varieties to diseases and climate stress.
But no hybrid varieties are available for many crops.
Referencing an article published in Nature Plants, thephys.org article looks into the reasons for this. It says:
Maize is a globally very important crop, and the use of hybrid varieties is routine. The first type was introduced as far back as 1930. But that hasn’t happened for other major crops such as wheat and cassava. Now, for the first time, a comprehensive study has been done of all the factors that determine whether commercial plant breeders can come up with a hybrid variety. Sometimes there are biological challenges. Often, economic factors come into play.
It’s a uniquely comprehensive survey, published in the journal Nature Plants. The authors of the article are associated with hybrid potato breeding company Solynta and Wageningen University & Research. The lead author is Emily ter Steeg, a Ph.D. candidate in development economics.
Ter Steeg explains that a hybrid variety is a descendant of two parental plants which complement each other perfectly. The hybrid then combines the best qualities of the parents
But to generate suitable parents,
“… you need to ensure that they are as genetically uniform as possible (homozygous). You can do this by crossing the parents with themselves—a process called ‘selfing’ or ‘inbreeding.’
“Developing strong parent lines takes time and costs money. So the plant breeder needs to be confident of getting a return on this investment.
First of the many obstacles to be overcome, it needs to be biologically possible to produce those homozygous parental lines. A self-pollinating plant is ideal, while it is much harder for plants that always cross-pollinate with another plant.
Moreover, some crops also have multiple sets of chromosomes, which makes it even harder, or close to impossible, to produce inbred parent lines.
The potato grown on our fields, for example, has four sets of chromosomes with hereditary material. That’s an important reason why there have been so few attempts to generate inbred lines. It makes potato breeding particularly difficult, and that’s why we still have ancient varieties like the Bintje or Russet Burbank.
But we’re making progress. There are in fact also diploid potatoes that have just a single set of genes. These varieties did not support inbreeding. But scientists at Solynta and Wageningen University & Research have recently managed to get around that obstacle. The Sli gene is the key to that. Now the path is clear to develop potatoes from hybrid seeds rather than from tubers.”
A subsequent study published in Nature is headed Genome evolution and diversity of wild and cultivated potatoes.
The abstract says potato (Solanum tuberosum L.) is the world’s most important non-cereal food crop, and the vast majority of commercially grown cultivars are highly heterozygous tetraploids.
The authors agree that advances in diploid hybrid breeding based on true seeds have the potential to revolutionise future potato breeding and production.
“So far, relatively few studies have examined the genome evolution and diversity of wild and cultivated landrace potatoes, which limits the application of their diversity in potato breeding.
“Here we assemble 44 high-quality diploid potato genomes from 24 wild and 20 cultivated accessions that are representative of Solanum section Petota, the tuber-bearing clade, as well as 2 genomes from the neighbouring section, Etuberosum.
“Extensive discordance of phylogenomic relationships suggests the complexity of potato evolution.”
The researchers found that the potato genome substantially expanded its repertoire of disease-resistance genes when compared with closely related seed-propagated solanaceous crops, indicative of the effect of tuber-based propagation strategies on the evolution of the potato genome.
“We discover a transcription factor that determines tuber identity and interacts with the mobile tuberization inductive signal SP6A.
“We also identify 561,433 high-confidence structural variants and construct a map of large inversions, which provides insights for improving inbred lines and precluding potential linkage drag, as exemplified by a 5.8-Mb inversion that is associated with carotenoid content in tubers.”
The authors say their study will accelerate hybrid potato breeding and enrich our understanding of the evolution and biology of potato as a global staple food crop.
Sources: Phys.org and Nature