Hallazgos encontrados en el estudio cualitativo

A snapshot of the root morphology at 15 and 25 days post excision shows similar branching zones as a proportion of the primary root length in all three of the genotypes is consistent for experiments I and II (Table 6). This is important because the

experimental regime was slightly modified for 47-9 in experiment I (refer section 3.2). Generally, the branching zone is approximately 50% of the primary root length for all three genotypes after 15 days post excision and approximately 80% after 25 days post excision when the plants are grown in P-sufficient media (Table 6). In experiment I, the branching zone was maintained between 85% and 90% from 30 days post excision in all of the genotypes (Figure 3.6d, e, and f). Interestingly, the supporting primary roots also have branching zones that are similar to the dominant primary root of each genotype (data not shown). The individual responses to P-supply differ between the genotypes however; there is a trend that suggests the elongation of the primary root and initiation of lateral roots changed in response to P-supply to achieve a branching zone between approximately 80% and 90% of the primary root length from 24 to 30 days post excision (Table 6).

Branching zone in 43-7

In 43-7, the dominant primary root length was 55 mm and 59 mm for experiments I and II respectively for the plants grown in P-sufficient media at 15 days post excision with similar dominant primary root lengths in the other two treatment groups after three days in low P or low S media (Table 6a). The branching zone was 55% and 51% respectively for experiment I and II. At 24 days post excision, the branching zone was between 78% and 84% because the number of lateral roots in the branching zone was proportional to the length (Table 6). At 35 days post excision (experiment I), the dominant primary root was significantly longer in the P-stressed plants, but the branching zone was maintained between treatment groups.

In summary, the branching zone is not affected by the nutrient supply in 43-7 because the number of lateral roots is proportional to the primary root length, and suggest that 43-7 equally sensitive to P-sufficient and low P media.

Table 6. Summary of dominant primary root development

Data from experiments (Expt) I and II in the dominant primary root at 15 and 25 days post excision for the different treatment groups. A. 43-7 B. 45-14, C. 47-9. The number of days pre- treatment is shown for each treatment group, and is broken down into the number of days in vermiculite and liquid media (+P) indicated respectively in superscript. *Significant differences between +P and –P were calculated using the student’s T-test (P< 0.05) and analysed using a minimum of five plants. There were no significant between –S and the other treatment groups. The term “growth” refers to the growth of the root post excision.

A. 43-7 Growth Expt Days pre treatment Days treated Media Length (mm) Branching zone Total lateral roots 15 I 15 (9 + 6) 15 +P 59 55% 12 II 9 (6 + 3) 6 +P 55 51% 13 II 9 (6 + 3) 6 -P 49 54% 11 II 9 (6 + 3) 6 -S 52 50% 10 25 I 15 (9 + 6) 10 +P 121 79% 36 I 15 (9 + 6) 10 -P 121 78% 33 II 9 (6 + 3) 15 +P 108 83% 31 II 9 (6 + 3) 15 -P 89 81% 25 II 9 (6 + 3) 15 -S 120 84% 35 35 I 15 (9 + 6) 20 +P 157 85% I 15 (9 + 6) 20 -P 192* 83%

B. 45-14 Growth Expt Days pre treatment Days treated Media Length (mm) Branching zone Total lateral roots 15 I 15 (9 + 6) 15 +P 105 44% 20 II 9 (6 + 3) 6 +P 114 67% 35 II 9 (6 + 3) 6 -P 110 63% 30 II 9 (6 + 3) 6 -S 110 68% 35 25 I 15(9 + 6) 10 +P 196 83% 65 I 15 (9 + 6) 10 -P 182 80% 58 II 9 (6 + 3) 16 +P 193 86% 82 II 9 (6 + 3) 16 -P 188 82% 80 II 9 (6 + 3) 16 -S 186 86% 73 36 I 15 (9 + 6) 21 +P 225 91% I 15 (9 + 6) 21 -P 249 87%*

C. 47-9 Growth Expt Days pre treatment Days treated Media Length (mm) Branching zone Total lateral roots 15 I 15 (9 + 6) 15 +P 52 54% 14 II 12 (7 + 5) 3 +P 27 54% 9 II 12 (7 + 5) 3 -P 38 61% 10 II 12 (7 + 5) 3 -S 28 64% 10 25 I 23 (9 + 14) 2 +P 88 85% 37 I 23 (9 + 14) 2 -P 101 82% 39 II 12 (7 + 5) 13 +P 76 78% 31 II 12 (7 + 5) 13 -P 77 89%* 44

Branching zone in 45-14

In 45-14, the dominant primary root length of the plants in P-sufficient media was similar after 15 days (post excision) in experiments I and II however, the branching zones were 44% and 67% for experiment I and II respectively (Table 6B). The higher branching zones were also observed in the low P and low S plants with three days treatment and is the result of the earlier transfer from vermiculite to P-sufficient media (as described in section 3.3). At 25 days post excision, the primary root length ranged between 182 mm and 196 mm and the branching zone ranged from 80% to 86% with 10 and 16 days treatment for experiments I and II respectively. A difference was observed in the number of lateral roots between the two experiments, at 15 and 25 days post excision. This is possibly due to the number of days in vermiculite (pre-treatment), because the numbers of lateral roots also differ between experiments I and II for the P- sufficient plants. In summary, the results suggest that 45-14 is sensitive to P-sufficient media because the branching zone increases in P-sufficient media (experiment II) and decreases in a low P supply (experiment I) (Figure 3.6e, Figure 3.7b, right and Table 6B).

Branching zone in 47-9

In 47-9, the length of the dominant primary root was 52 mm in experiment I after nine days in vermiculite and six days in P-sufficient media at 15 days post excision.

In experiment II (15 days post excision), the dominant primary root length was 27 mm after seven days in vermiculite and eight days in P-sufficient media but the branching zone was 54% for both experiments, which means the lateral root density was higher in experiment II (Table 6C). In experiment II, the P-stressed plants had three days

treatment at 15 days post excision, and although not significant, the stimulatory response is evident in the P and S treatment groups. At 25 days post excision, the primary root length was similar, and the branching zone was significantly higher in experiment II with 13 days treatment. In experiment I, the P-supply was reduced after 23 days post excision when the branching zone approached 80% of the primary root length, and the stimulatory response occurred in the P-stressed roots.

However, the branching zone was above 80% of the primary root length and similar between treatment groups. At 40 days post excision, the P-stressed roots were longer than the P-sufficient roots in experiment I, but there was no difference in the branching zone that increased by 2% (+P) and 6% (-P) from 25 days post excision.

In summary, the results suggest that 47-9 is sensitive to low P media, and low S media because the branching zone increases by elongating the primary root and increasing the number of lateral roots.