Elucidation of Physio-Chemical Mechanism Associated with Banana Paper In The Management Of Potato Cyst Nematodes
Ochola, Juliet Akoth
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Potato production in Kenya is threatened by the occurrence of the widespread potato cyst nematode (PCN), which causes yield losses of more than 80%. Recent attempts to assess novel management options for PCN in the country demonstrated the effectiveness of the “Wrap & Plant” (W&P) technology to increase yields under heavy PCN infestations. This innovation consists of a field deployable biodegradable matrix produced from banana fibre (banana paper) that is impregnated with abamectin (nematicide). Farms where potato seeds were wrapped with the abamectin-treated and the untreated banana paper (paper control) increased yields by 4-fold and 3-fold, respectively, and showed decline of 83% and 43% of the PCN inoculum in the soil. The current study sought to elucidate the underlying mechanism associated with the banana paper in management of PCN. We hypothesised that banana paper acts as a physical and/or chemical barrier, hampering plant-nematode communication, which is important for PCN hatching and host infection. Behavioural experiments indicated that the untreated and treated banana paper reduced PCN hatching by 60% and 80%, respectively. The banana paper also inhibited chemotactic response of the PCN juveniles, reducing their attraction by 99 and 94% in treated and untreated banana paper, respectively. An evaluation of the effect of the banana paper on PCN development using pot trials also showed a reduction in formation of females when the potatoes were wrapped with the banana paper compared to when potatoes were not wrapped, suggesting a lowered reproduction rate in wrapped plants. Chemical analysis by ultra-performance liquid chromatography, coupled to triple quadrupole mass spectrometry (UPLC-QqQ-MS) of the potato root exudates (PRE) detected the tetranortriterpene solanoeclepin A (2), steroidal glycoalkaloids α-solanine (3) and α-chaconine (4); the steroidal alkaloids solanidine (24), solasodine (27), and tomatidine (28); phytohormones, zeatin (10) and methyl dihydrojasmonate (23); and amino acids, tryptophan (22), tyrosine (20) and phenylalanine (21). Of these compounds, the steroidal glycoalkaloids and steroidal alkaloids showed hatch stimulating activity when tested on PCN G. rostochiensis. Potato root exudate exposure to banana paper, revealed that the paper matrix adsorbs most of the PRE components inclusive of the identified PCN hatching factors. Further experiments to understand the interaction between the banana paper and PRE showed a similar interaction between pure cellulose powder and PRE, suggesting that adsorption of the polar components of the PRE by hydrogen bonding on the cellulose matrix of the banana paper could be the mechanism underlying the observed effect. This research provides new insights on how PCN could be managed at the rhizosphere level by disrupting the chemical signalling with its hosts plant using a lignocellulosic matrix that can adsorb the hatching semiochemicals.