“Understanding Environmental Modulation of Heterosis”

UNIVERSITY OF AGRICULTURAL SCIENCES, BANGALORE

DEPARTMENT OF GENETICS AND PLANT BREEDING

SEMINAR – GPB 681 (0+1)

“Understanding Environmental Modulation of Heterosis”

    Heterosis, or hybrid vigor, is the superior performance of hybrid offspring compared to the average of their parents. This phenomenon has been widely exploited in both plant and animal breeding for centuries. Research has focused on the molecular basis of heterosis, as well as on the variation in the degree of heterosis among different parental combinations. Interestingly, heterosis for a given trait within the same parental combination can vary substantially depending on environmental conditions. For instance, high heterosis may be observed for yield, but little to no heterosis for plant height. Therefore, understanding the environmental modulation of heterosis is critical for its effective utilization in crop improvement.

    A comprehensive study in rice involving 140 crosses and 17 parents evaluated in six environments, created by three nitrogen fertility levels (0, 60, and 120 kg N/ha) across two seasons (wet and dry), revealed significant heterosis, heterobeltiosis, and standard heterosis across environments. The magnitude of heterosis was greater in the wet season (stressful environment) compared to the dry season (favorable environment), highlighting the strong influence of environmental factors on heterotic expression (Young and Virmani, 1990).

    Similarly, physiological investigations in maize revealed that heterosis for grain yield was more pronounced under shade stress during the pre-silking and silking stages than under normal conditions. This was largely due to increased heterosis for both harvest index and total dry matter (TDM). In contrast, shading during grain filling did not significantly enhance heterosis for yield. Kernel number was identified as a major contributor to heterotic yield performance under shading stress (Liu and Tollenaar, 2009).

    Overall, heterosis tends to be amplified under stress conditions because inbred parents suffer more from stress than hybrid offspring. As breeders and geneticists aim to exploit heterosis, it is crucial to recognize that heterotic performance is not fixed for a specific parent–hybrid combination. Instead, it is highly dynamic and modulated by environmental conditions, necessitating careful evaluation across multiple environments for effective crop breeding.

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References

1. Li, Z., Coffey, L., Garfin, J., Miller, N.D., White, M.R., Spalding, E.P., De Leon, N., Kaeppler, S.M., Schnable, P.S., Springer, N.M. and Hirsch, C.N., 2018. Genotype-by-environment interactions affecting heterosis in maize. PLoS One, 13(1):191–221.

2. Liu, W. and Tollenaar, M., 2009. Physiological mechanisms underlying heterosis for shade tolerance in maize. Crop Sci., 49(5):1817–1826.

3. Young, J. and Virmani, S.S., 1990. Heterosis in rice over environments. Euphytica, 51:87–93.

4. Zaidi, P., Maniselvan, P., Sultana, R., Yadav, M., Singh, R., Singh, S., Dass, S. and Srinivasan, G., 2007. Importance of secondary traits in improvement of maize (Zea mays L.) for enhancing tolerance to excessive soil moisture stress. Cereal Res. Commun., 35(3):1427–1435.