Researchers Find Yield Differences in Hybrid Crops

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Progressive heterobeltiosis for bunch weight in bred ‘Matooke’ banana hybrids (NARITAs). A: ‘Entukura’ (3x female grandparent), B: ‘1438K-1’ (4x female parent) and C: ‘NARITA 17’ (3x hybrid)
Hybrid crops are expected to have higher edible yields than their parents, but by how much?

A team of researchers comparing the performance of the East Africa Highland banana, locally known as ‘Matooke’, found that some hybrids had bunch weights that were up to two and a half times heavier than those of their best-performing parents!

This significant yield difference is perhaps the highest among the main food crops.

The scientists were studying a phenomenon known as “heterobeltiosis,” defined as the hybrid performance being superior to that of their best performing parent.

Scientists wanted to quickly identify parents with the greatest chances of producing offspring with higher bunch weight and stature for the banana breeding programs.

The study assessed heterobeltiosis in bunch weight and height of cross-bred ‘Matooke’ hybrids known as NARITAs that were developed by Uganda’s National Agricultural Research Organisation (NARO) and International Institute of Tropical Agriculture (IITA) following 18 years of research.

Early in November 2014, NARO and IITA released the first report on the preliminary performance trials of the first-ever hybrid varieties of the East Africa highl and banana, jointly developed by the two organizations for food and juice.

From the trial results, these hybrid varieties known as NARITA (NARO-IITA), performed better than the local check across all traits being evaluated. For example, 96% of the hybrids had a bunch weight greater than that of the local check. The bunch weight varied up to 28.4 kg, with an overall mean of 18.3 kg.

The hybrids were developed from over 20 years of research to address the major threats to the crop’s production in East and Central Africa including pests (banana weevils and nematodes) and diseases (Fusarium wilt and black Sigatoka) that resulted in the currently low yield in smallholder farmers’ fields. This in turn has had a negative impact on food security and the income of millions of smallholder farmers.

In Uganda, for example, banana occupies the largest cultivated area among staple food crops with more than 75% of farmers growing it.

The evaluation of 25 out of 27 existing NARITA hybrids (18 for food and seven for juice), was conducted at Namulonge in central Uganda. The hybrids were evaluated for performance, adaptability, and stability against local East Africa highland bananas.

The preliminary results, therefore, show that these hybrids have potential to increase banana production in Uganda, Tanzania, and the highlands of East Africa. Further testing is now planned in Uganda and Tanzania across multiple locations and involving farmers to assess performance on farmers’ fields.

In the study, the growth and yields of the NARITAs were monitored alongside their parents and grandparents in Uganda for 4 years. While not much difference was noted in height, over half of the NARITAs showed increased bunch weights.

The highest heterobeltiosis for bunch weight was 249% increase versus its ‘Matooke’ grandmother and 136% against its primary tetraploid hybrid parent, for the secondary triploid NARITA 17.

“Such significant heterobeltiosis exhibited for bunch weight is, to our knowledge, the largest among main food crops. Since bananas are vegetatively propagated, the effect of heterobeltiosis is easily fixed in the hybrids and will not be lost over time after the release and further commercialization of these hybrids,” says Michael Batte, associate banana researcher at the International Institute of Tropical Agriculture (IITA)-Uganda and the corresponding author of the study, published in the paper, Significant Progressive Heterobeltiosis in Banana Crossbreeding, in the BMC Plant Biology journal on 29 October 2020.

In Uganda, at least 75% of farmers grow ‘Matooke’ and other bananas on an estimated 38% of the total cultivated land.

However, production has declined over the past three decades, mainly due to declining soil fertility, drought and attacks by pathogens, such as banana bacterial wilt, black Sigatoka or black leaf streak disease, and fusarium wilt or Panama disease, and pests including the banana weevil or burrowing nematode.

Breeding of resistant cultivars is the most sustainable intervention for managing these pathogens and pests in the Great Lakes Region of Africa and elsewhere. However, banana breeding is a lengthy process, with new hybrids that are acceptable to consumers taking over two decades to deliver.

Efficient selection of parents that have the traits to produce superior hybrids within a shorter time period would therefore be highly desirable.

This collaborative study between IITA and the Swedish University of Agricultural Sciences (SLU) has provided a very important milestone in understanding heterobeltiosis, a characteristic that helps in selecting breeding material with high complementarity, thus increasing the efficiency of banana breeding.

The work is supported by the Bill & Melinda Gates FoundationCGIAR Fund and, in particular, the CGIAR Research Program for Roots, Tubers, and Bananas (CRP-RTB).

 

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