Characterization of Lateral Root Development at the Onset of Storage Root Initiation in ‘Beauregard’ Sweetpotato Adventitious Roots

Abstract

<jats:p>This study characterized lateral root (LR) development attributes during the onset of storage root (SR) initiation stage in ‘Beauregard’ sweetpotato. SR initiation has been defined as the appearance of cambia around the protoxylem and secondary xylem elements. Our results showed that 20-day-old adventitious roots (ARs) classified as SRs had 53% and 85% greater mean LR count than pencil roots (PRs) and lignified roots (LGs), respectively. SRs had 53% and 78% greater mean LR density relative to PRs and LGs, respectively. SRs had 66% and 130% greater mean total LR length than PRs and LGs, respectively. SRs had lower mean main root (MR)/LR length ratio compared with PRs (–38%) and LGs (–60%). SRs had 70% and 134% greater mean surface area than PRs and LGs, respectively. SRs had lower mean MR/LR surface area ratio compared with PRs (–42%) and LGs (–62%). The plot of the first and second principal components revealed the presence of a gradient between extreme LG and SR clusters, suggesting a developmental transition between LGs and SRs with PRs representing an intermediate developmental stage. Although AR architecture is not the sole determinant of SR formation, our data help provide a basis for integrating AR architecture attributes with other factors that are known to influence SR initiation. Growth substrate moisture variability influenced LR development during the critical SR initiation period. Relative to the control treatments, water deprivation 10 to 20 days after transplanting (DAT) reduced mean LR count, length, and surface area by 49%, 103%, and 94%, respectively. Saturated conditions 10 to 20 DAT reduced mean LR count, length, and surface area by 75%, 81%, and 77%, respectively. These results represent the first evidence for the association between anatomical cues of SR initiation and root architecture and provide corroborating data that soil moisture variability 10 to 20 DAT directly influences SR yield potential through AR architecture modifications that are associated with diminished SR formation. This information can be used to further optimize SR yield by identifying agroclimatic and management variables that are associated with desirable LR development during the critical SR initiation stage.</jats:p>

Variation in Virus Symptom Development and Root Architecture Attributes at the Onset of Storage Root Initiation in ‘Beauregard’ Sweetpotato Plants Grown with or without Nitrogen

“…First, the presence of a complex of viruses (SPFMV, SPVG, SPVC, and SPV2) was associated with the reduction of adventitious root number, regardless of the presence of nitrogen. Secondly, the presence of the phloem-restricted virus, SPCSV, was associated with the reduction in LR length, number, and density, previously associated with increased lignification in the stele, thereby preventing storage root initiation [8]. Both of these situations result in the net reduction of adventitious roots that can undergo storage root initiation and subsequent bulking, thereby negatively impacting yield potential.…”

“…Intact adventitious roots that were 20 cm or greater in length were floated on waterproof trays and scanned using a specialized Dual Scan optical scanner (Regent Instruments Inc., Quebec, Canada). Based on previous work, adventitious roots that were less than 20 cm in length generally failed to show anatomical features associated with lignification or storage root initiation [6], [8]. The acquisition and image analysis software was WinRHIZO Pro (v. 2009c; Regent Instruments Inc.).…”

Root System Architecture and Abiotic Stress Tolerance: Current Knowledge in Root and Tuber Crops

“…Recent work demonstrated the link between LR development and lignification. In ARs with a prevalence of arrested or non-emerged LR primordia, the adjacent stelar tissue becomes lignified thus rendering it incapable of undergoing swelling due to the absence of vascular and anomalous cambia development (Villordon et al, 2012). The precise relationship between stele lignification and LR development is still not clear in sweetpotato.…”

“…In sweetpotato for example, the final storage root yield depends on the capacity of a genotype to develop LRs on the main ARs. Those with arrested or non-emerged LRs develop lignified steles, which inhibit localized swelling into storage roots (Villordon et al, 2012). Other Important contributors to RSA include single-cell projections from root epidermal cells referred to as root hairs (Tanaka et al, 2014).…”

Molecular Regulation of Storage Root Formation and Development in Sweet Potato

“…In addition to the aforementioned four types of roots, lateral roots (primary, secondary, and occasionally tertiary) are also formed in nonstorage fibrous roots, nonstorage, thick lignified fibrous roots, lignified pencil roots, and starch-accumulating storage roots (Pardales et al 1999;Tanaka et al 2005Tanaka et al , 2008Villordon et al 2012).…”