Abstract
Leaf spot is one of the most important cassava diseases. Nanotechnology can be applied to control diseases and improve plant growth. This study was performed to prepare chitosan (CS) nanoparticle (NP)-loaded salicylic acid (SA) or silver (Ag) by the ionic gelation method, and to evaluate their effectiveness on reducing leaf spot disease and enhancing the growth of cassava plants. The CS (0.4 or 0.5%) and Pentasodium triphosphate (0.2 or 0.5%) were mixed with SA varying at 0.05, 0.1, or 0.2% or silver nitrate varying at 1, 2, or 3 mM to prepare three formulations of CS-NP-loaded SA named N1, N2, and N3 or CS-NP-loaded Ag named N4, N5, and N6. The results showed that the six formulations were not toxic to cassava leaves up to 800 ppm. The CS-NP-loaded SA (N3) and CS-NP-loaded Ag (N6) were more effective than the remaining formulations in reducing the disease severity and the disease index of leaf spot. Furthermore, N3 at 400 ppm and N6 at 200, 400, and 800 ppm could reduce disease severity (68.9–73.6% or 37.0–37.7%, depending on the time of treatment and the pathogen density) and enhance plant growth more than or equal to commercial fungicide or nano-fungicide products under net-house conditions. The study indicates the potential to use CS-NP-loaded SA or Ag as elicitors to manage cassava leaf spot disease.
Highlights
The cassava (Manihot esculenta Crantz) plant and its tapioca are an important food source for world food security, especially in developing countries
CS-NPloaded Ag was synthesized by the ionic gelation method with a size of 90.29 nm and a zeta potential of +92.05 mV with antibacterial properties that apply in medical applications [29]
The leaf disk assay method confirmed that CS-NP formulations up to 800 ppm do not cause toxicity on cassava leaves
Summary
The cassava (Manihot esculenta Crantz) plant and its tapioca are an important food source for world food security, especially in developing countries. Thailand’s cassava acreage and production reached 1.34 million hectares and 30.84 million tons in 2017, which has increased 1.15-fold over the previous ten years. Thailand’s acreage and production account for only 5.45% and 11.04% of the world, respectively, the quantity and value of Thailand’s cassava crop are between 58.5–81.2% and 44.4–56.7% in the world export market, respectively. Cassava is Thailand’s key export crop [2]. The biotic stress on a living organism including plant diseases, insects, and weeds, or abiotic stress, such as adverse environmental factors, could affect the growth and development of cassava, resulting in loss of yield. Twenty-eight types of cassava diseases caused by fungi, viruses, or bacteria have been recorded [3,4].
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