Underground heterosis for yield improvement in melon

Authors: DAFNA, ASAF - Newe Ya'Ar Research Center; HALPERIN, ILAN - Newe Ya'Ar Research Center; OREN, ELAD - Newe Ya'Ar Research Center; ISAACSON, TAL - Newe Ya'Ar Research Center; TZURI, GALIL - Newe Ya'Ar Research Center; MEIR, AYALA - Newe Ya'Ar Research Center; SCHAFFER, ARTHUR - Volcani Center (ARO); BURGER, JOSEPH - Newe Ya'Ar Research Center; TADMOR, YAAKOV - Newe Ya'Ar Research Center; Buckler, Edward - Ed; GUR, AMIT - Newe Ya'Ar Research Center

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2021
Publication Date: 9/30/2021
Citation: Dafna, A., Halperin, I., Oren, E., Isaacson, T., Tzuri, G., Meir, A., Schaffer, A.A., Burger, J., Tadmor, Y., Buckler IV, E.S., Gur, A. 2021. Underground heterosis for yield improvement in melon. Journal of Experimental Botany. 72(18):6205-6218. https://doi.org/10.1093/jxb/erab219.
DOI: https://doi.org/10.1093/jxb/erab219

Interpretive Summary: Improving melon yields while maintaining fruit quality is an ongoing challenge. Heterosis—the superiority of hybrids over their parents—is a powerful phenomenon, associated with plant fitness and crop yield enhancement. Heterosis is often correlated with the diversity between the parents; the problem being that the same diversity can have adverse effects on other desirable traits of the final product. We show, using an exhaustive mating scheme called diallel, that yield heterosis is a meaningful phenomenon in hybrid melons that can be maintained using grafting. Using a superior hybrid as a rootstock, grafted with a commercial variety as a scion, increases yield while preserving desired fruit quality traits.

Technical Abstract: Heterosis, the superiority of hybrids over their parents, is a major genetic force associated with plant fitness and crop yield enhancement. Understanding and predicting heterosis is crucial for evolutionary biology, as well as for plant and animal breeding. We investigated root-mediated yield heterosis in melons (Cucumis melo) by characterizing common variety grafted onto 190 hybrid rootstocks resulting from crossing 20 diverse inbreds in a diallel-mating scheme. Hybrid rootstocks improved yield by more than 40% compared to their parents and the best hybrid outperformed the reference commercial variety by 65% under both optimal and minimal irrigation treatments. To characterize the genetics of the underground heterosis we conducted whole-genome re-sequencing of the 20 founder lines, and showed that parental genetic distance was no predictor for the level of heterosis. Through inference of the 190 hybrids genotypes from their parental genomes, followed by genome-wide association analysis, we mapped multiple root-mediated yield QTLs. The yield enhancement of the four best-performing hybrid rootstocks was validated in multiple experiments with four different scion varieties. While root biology is receiving increased attention, most of the research is conducted using plants not amenable to grafting and, as a result, it is difficult to separate root and shoot effects. Here, we use the rich genetic and genomic resources of Cucumis melo, where grafting is a common practice, to dissect a unique phenomenon of root-mediated yield heterosis, by directly evaluating in the field the contribution of the roots to fruit yield. Our grafting approach is inverted to the common roots genetics research path that focuses mainly on variation in root system architecture rather than the ultimate root-mediated whole-plant performance, and is a step towards discovery of candidate genes involved in root function and yield enhancement. Highlight: We show that yield heterosis is significant in melon and controlled independently above and underground. Using common-scion grafting approach, we find that heritable rootstock-mediated variation in a diallel population is associated with substantial fruit yield heterosis.