Grafting of Black Pepper onto Native Piper Species

Brazil is the third largest producer of black pepper in the world. Although Brazil is prominent in black pepper production, the average yield is low. The main stressful factors in Brazilian black pepper crops directly affect the root system, such as water deficit, flooding and diseases. One strategy to enable the cultivation of black pepper in contaminated areas is the planting of seedlings grafted onto wild Piper species resistant to fusariosis, drought or flooding. Grafting consists of the union of plant tissues from at least two different plants to generate a single organism. However, many factors influence graft incompatibility, the main ones being botanical affinity, which is directly linked to genetic and morphological factors, environmental conditions and physiological factors. The objective of this work was to investigate the compatibility and physiology of grafted seedlings of 'bragantina' black pepper, using three rootstocks. The experiment was conducted at the Linhares Experimental Farm, of the Capixaba Institute for Research, Technical Assistance and Rural Extension. Piper aduncum, Piper caldense and the cultivar bragantina (Piper nigrum) were evaluated as rootstock. The native species were propagated by seeds and the bragantina cultivar by cuttings, both propagules collected from mother plants in the Active Germplasm Bank located on the farm. The full cleft top method was carried out. The rootstocks were decapitated just below the fourth node, in which a slit was made, 3 cm deep, and after insertion of the graft, it was tied with a rubber band. The grafts were covered with plastic bags. After grafting, the plants were kept in a nursery. Four months after grafting, survival, chlorophyll a fluorescence, gas exchange, hydraulic conductivity of the stem and root, shoot and root anatomy were assessed. At the end of the experiment, the survival rate was higher in plants grafted onto Piper caldense. P. aduncum showed an increase in the number of active FSII reaction centers by cross sections (RC/CS0). The photosynthetic performance index relative to absorption (PIabs) was increased in P. aduncum. P. caldense and bragantina showed no significant difference. Water use efficiency (WUE) was higher in P. caldense plants, followed by bragantina plants. P. aduncum showed a decrease in WUE. P. aduncum showed an increase in the length of the vascular bundle and root xylem, however P. caldense showed reduced values. Regarding the number of root xylem vessels, the highest values were observed in bragantina plants. The diameter of the root xylem vessels was higher in P. aduncum. P. caldense and bragantina showed no difference. It is concluded that among the species studied, P. caldense was the species that presented the most characteristics that make it compatible with being used as a rootstock using the bragantina genotype as a graft.