Interactive and dynamic effects of rootstock and rhizobiome on scion nutrition in cacao seedlings

Authors: SCHMIDT, JENNIFER - M & M Mars Company - United States; DUVAL, ASHLEY - M & M Mars Company - United States; Puig, Alina; TEMPELEU, ALEXANDRA - M & M Mars Company - United States; CROW, TAYLOR - M & M Mars Company - United States

Submitted to: Frontiers in Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2021
Publication Date: 11/18/2021
Citation: Schmidt, J., Duval, A., Puig, A.S., Tempeleu, A., Crow, T. 2021. Interactive and dynamic effects of rootstock and rhizobiome on scion nutrition in cacao seedlings. Frontiers in Agronomy. 3:754646. https://doi.org/10.3389/fagro.2021.754646.
DOI: https://doi.org/10.3389/fagro.2021.754646

Interpretive Summary: Improved cacao clones developed by breeding programs are primarily propagated through grafting, which usually uses rootstock grown from seeds of open-pollinated pods. Grafting creates a genetic clone of the original plant and allows growers to maintain specific traits such as high yield, fruit quality, and disease resistance. Although the importance of using rootstock with resistance to soil-borne diseases, such as Ceratocystis, is well understood in cacao, the impact of rootstock on nutrient uptake has not been examined. A greenhouse study was conducted to better understand the relationships among rootstock and scion identities, rhizobiome composition, and plant uptake of nutrients. Results showed that the microbial population in the rhizosphere influences plant nutrient uptake, and identified taxa that may be influencing this interaction. These associations were more strongly influenced by rootstock genotype than by the scion. This research improves the understanding of how rootstock and scions affect root-microbe interactions and nutrient acquisition, and may lead to improved rootstock selection and breeding. The use of improved rootstock for cacao propagation could contribute to efforts to increase yield per area and improve adaptation to low quality soils.

Technical Abstract: Perennial agroecosystems often seek to optimize productivity by breeding nutrient-efficient, disease-resistant rootstocks. In cacao (Theobroma cacao L.), however, rootstock selection has traditionally relied on locally available open pollinated populations with limited data on performance. Furthermore, rootstock associations with the rhizobiome, or rhizosphere microbiome, have been neglected. Better understanding of rootstock and scion effects on cacao-specific traits, particularly those involved in root-microbe interactions and nutrient acquisition, could contribute to more efficient rootstock selection and breeding. A rootstock-scion interaction study was conducted using three scion genotypes and eight rootstock populations under greenhouse conditions to better understand the relationships among rootstock and scion identities, soil fertility, and rhizobiome composition and the impacts of these factors on plant uptake of macro- and micronutrients. We show that rootstock genotype has a stronger influence than scion on nutrient uptake, bacterial and fungal diversity, and rhizobiome composition, and that the relative contributions of rootstock and scion genotype to foliar nutrient status are dynamic over time. Correlation analysis and stepwise regression revealed complex relationships of soil physicochemical parameters and the rhizobiome to plant nutrition and emphasized strong impacts of microbial diversity and composition on specific nutrients. Linear discriminant analysis effect size estimation identified rootstock-responsive taxa potentially related to plant nutrition. This study highlights the importance of considering root-associated microbial communities as a factor in cacao rootstock breeding and the need for further investigation into mechanisms underlying nutrient acquisition and microbial interactions in grafted plants.