Multipronged Phenotyping Approaches to Characterize Sugarcane Root Systems

As a primary conductor of water and nutrients, roots are indispensable for growth and development. A thorough understanding of the root system is important for sugarcane as it takes a year to complete its lifecycle. The holistic approach here integrates the viable platforms for the phenotyping, and this will benefit in advancing the knowledge of sugarcane root systems and their responses to address the work conditions.

This methodology is specific to the sugarcane crop as it has a unique root system as a long crop. However, with minor modifications, this method may be adapted to other crops. To begin, raise the commercial sugar cane hybrids or varieties in the field using two butted sets planted at a row spacing of 120 centimeters and 90 centimeters within the rows.

Follow the recommended package of practices to ensure good crop establishment and growth. At the end of the maturity phase, employ an excavator to dig a trench of 1.5 meters deep and 1.0 meters wide in the field. Clear the soil from the root zones without damaging the roots with continuous water jetting.

Once the adhering soil loosens due to jetting, uproot the cane along with the root system and take it to the laboratory for manual measurement of the growth parameters, namely the number of roots, root length, volume, and weight. Use a cylindrical root core sampler of 61 centimeters in height, 16 centimeters in diameter, weighing eight kilograms and fabricated using mild steel or MS material for sugarcane root sampling in the field. It is provided with a sharp edge at the bottom for easy penetration and has collars of three centimeters in diameter at the top to lift the sampler.

At the maturity phase of the commercial sugar cane crop, fasten the top edge of the sampler to the primary chute or cane and hammer continuously to reach the desired soil depth of 45 centimeters. Then lift the entire soil mass into the sampler and wash it carefully under running water to separate the adhering roots. Measure the physical parameters of the plant, like plant height and leaf area in the laboratory.

Then spread the roots on transparent trays for scanning and analyzing the corresponding digitized images using the software. Construct a root phenotyping structure comprising three adjacent compartments of 4.5 meters by 10.1 meters for sampling the sugar cane roots. Make provision for manually dismantling the sidewalls to reveal the underground root system up to a depth of 80 to 100 centimeters.

Fill and compact the structure with field soil, leaving a head space of around 20 centimeters and having adequate drainage holes to facilitate soil aeration. Salve the bud chips of germplasm clones comprising saccharum officinarum, saccharum spontaneum, saccharum barberri, saccharum sinense, and saccharum robustum. Allow them to germinate for 30 days in per trays, comprising rooting media.

After 30 days of germination transplant the uniform and healthy settlings to the structure in the rows with a spacing of 90 centimeters and 60 centimeters distance within rows. Follow the recommended POP to ensure good crop establishment and growth. During the formative phase of 60 to 120 days after planting and the grand growth phase of 120 to 150 days after planting, manually remove the sidewalls made of the precast slabs before continuously spraying the water jet to expose the roots.

Uproot the entire root system and transfer it to the laboratory to measure the physical parameters. Then spread the roots on transparent trays for scanning and analyzing the corresponding digitized images in software. To study the rhizosphere biology and the finer details of root biology, fabricate an in-house hydroponic system in an environment controlled glass house conducive to sugar cane growth.

In the 20 by 20 by 50 centimeters dimensions tanks with aquarium pumps for aeration, add around 15 liters of modified Hoagland's Nutrient Solution. Sell the bud chips of sugarcane varieties and saccharum species clones and allow them to germinate for 30 days in the per trays, comprising composted core pith before transplanting the uniform and healthy settlings to hydroponic tanks at the frequency of three settlings per tank. After 60 days when the germination phase ends, immerse the roots of intact plants in 50 milliliters of sterile double distilled water or trap solution for four hours, and collect the root exudates during the peak photosynthetic activity.

Assess the activity of the enzymes, peroxidase, and superoxide dismutase and total phenolic content in the third month according to standard protocol. Finally, assess the response to root injury by inflicting a longitudinal slice in the primary root up to the root tip using a sterile surgical blade and monitor the changes periodically. In the root phenotyping, the longer roots of CO 62175 demonstrated a superior root system for cumulative root length, root surface area, root volume, and average root diameter.

Saccharum species showed significant variations in morphological traits during the formative phase. Saccharum spontaneous had the highest cumulative root length per clump, while saccharum sinense showed the lowest. Saccharum spontaneum showed the highest root surface area, root dry weight, root volume, and the root to shoot ratio.

Saccharum robustum showed the highest root volume and root diameter. Anatomical studies revealed that long root hair schlerenchymidis exodermis reduced cortical cell layers, increased cortical oerinchma, and increased steel area and xylem vessel number with large diameter were beneficial under drought conditions, whereas under water logging stress, increased root diameter and higher cortical cell area with increased aerenchymidis cells were observed. Saccharum robustum showed the highest total carboxylate exudation while the lowest exudation was recorded in saccharum spontaneum.

In sugarcane varieties, a significant difference in the root hair density was observed with variation in shape and pigmentation of the root cap. The highest peroxidase activity and total phenolic content were present in C086032, and the lowest in C062175. During rejuvenation studies, Cox 671 showed the appearance of secondary roots in three days and Co-06022 took 10 days with symptoms of senescence on the third day.

We need to exercise caution while interrupting the results obtained from individual protocol. An institute study of root system is ideal for sugar cane, but control platforms may be useful for specialist purposes. Understanding various aspects of root phenotype is essential to releasing the sugar cane varieties.

Automating the techniques and integrating big data analytics or artificial intelligence to interpret the results would broaden our expertise in the field. Of the results, in characterizing root system traits under normal and periodic stress situations have paved the way for exploratory research areas like root plasticity, radiant nutrientisms, and miotic stresses.