Table 1.
Characteristics of cassava varieties used for the validation of the seed treatment technology under field conditions.
Fig 1.
Depiction of cassava seed pieces (16 and 8 cm), untreated (left) and treated (right) with the seed treatment formulation, as used in this work.
Table 2.
Locations of field trials including institution names, coordinates and altitude.
Table 3.
Composition of seed treatment formulations used in Brazil and Uganda.
Fig 2.
Effect of the seed treatment on plantlets of varieties ‘Cascuda’ and ‘Fécula Branca’, 30 days after planting in growth chambers.
In (A) and (C), different cutting sizes are shown, 8 and 16cm, both with and without the treatment. Underlying parameters for shoot and root length are listed in (B) and (D). Phytotoxicity (%), germination (%), plant height (cm), shoot dry weight (g) and root dry weight (g) are shown in (E). Values displayed represent averages across 3 replicates with 20 samples per plot each. Error bars depict standard errors. Different letters per variety indicate significant differences between cutting sizes, both with and without treatment, p < 0.05 by LSD test.
Fig 3.
Results from experiments performed in Uganda, using two local varieties (NASE 19’ and ‘NAROCASS 1’) and in Brazil, using three local varieties (‘BRS Formosa’, ‘Cascuda’ and ‘Fécula Branca’).
Seed pieces with lengths of 12 and 24 cm (Uganda) and 8 and 16 cm (Brazil) under treated and control conditions were compared. Treatment formulations are explained in Table 3. Germination percentage was assessed 30 days after planting. Values are averages across 4 replicates of 4 plots (with 81 plants per plot) each. Error bars represent standard deviation. Statistical analysis was performed with a t-test, assuming unequal variances. Significance levels depicted are as follows: n.s.: non-significant; *: p < 0.05; **: p < 0.01; ***: p < 0.005.
Fig 4.
A) Plant coverage (%) of varieties ‘BRS Formosa’ and ‘IAC90’, evaluated 60 days after planting under field conditions. Rows are grouped in plots of 8 cm and 16 cm seed piece length, respectively. Columns are depicted correspondingly to applied treatment; treated or control (treated only with water), as marked on the top of each column. In B), the corresponding cover crop percentages are depicted for both of the varieties which have been trialled, as well as for the different lengths and treatments. Values are averages across 4 replicates of 10 samples per plot. Error bars represent standard error. Different letters for each variety indicate significant differences between cutting sizes, both with and without the treatment, p < 0.05 by LSD test.
Fig 5.
Parameters from the field trials for the varieties ‘BRS Formosa’ and ‘Cascuda’, harvested and evaluated 12 months after planting.
Assessed parameters include plant stand (%); plant height (m), above-ground biomass (t ha-1) and fresh root yield (t ha-1). Treated and untreated seed pieces of lengths 8 and 16 cm are compared. Values are averages across 4 replicates of 20 samples per plot and three environments in Northeast Brazil (Embrapa, UFRB, Bahiamido). Error bars represent standard error. Different letters for each variety indicate significant differences between different cutting sizes, both with and without the treatment, p < 0.05 by Tukey Honest Significant Difference test.
Fig 6.
Generalised model of the cassava seed system.
In A), a generalised cassava seed system is shown. The initial year in multiplication consists of tissue culture production (Nuclear, 1) and subsequent plantlet multiplication in a greenhouse (Pre-Basic, 2). Further, the basic seed multiplication cycle (Basic, 3) and the certified cycles (Certified, 4–6) are entered, each with the duration of one year. In the basic cycle, shoot plantlets are planted, after one year of basic seed multiplication, cassava seed stems can be used. The resulting multiplication factor, depending on seed piece length is depicted on the right. For the basic and first certified cycles (3 and 4), the multiplication factors can be double the factors of the two last certified cycles (5 and 6), as intensive crop systems associated with the use of irrigation allow two stem harvests per year. A full iteration through the entire seed system equals 5 years. Multiplication factors are indicated per year, based on entering the seed system with one single tissue culture plantlet. Asterisks depict where the treatment technology is recommended for application. From the greenhouse multiplication step onwards, a benefit from the technology’s use is expected. In B), the seed piece production is shown over the full duration of five years. Production for the three different lengths (8, 16, and 24 cm) is depicted. The dashed line shows the equal amount of seed pieces for 8 cm after 4 years and for 16 cm after 5 years, 147’456 seed pieces.